Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $179.26   10.403%   $197.9084   $197.91   $197.90   $197.90  
  Purchase #2 $222.57   9.315%   $243.3024   $243.30   $243.30   $243.30  
  Purchase #3 $181.81   12.343%   $204.2508   $204.25   $204.25   $204.30  
  Purchase #4 $107.37   11.606%   $119.8314   $119.83   $119.85   $119.80  
  Purchase #5 $219.29   12.536%   $246.7802   $246.78   $246.80   $246.80  
  Purchase #6 $209.95   12.742%   $236.7018   $236.70   $236.70   $236.70  
  Purchase #7 $116.84   3.177%   $120.552   $120.55   $120.55   $120.60  
  7 purchase totals = $1,237.09       $1,369.3270   $1,369.32   $1,369.35   $1,369.40