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 $196.72   7.112%   $210.7107   $210.71   $210.70   $210.70  
  Purchase #2 $226.80   4.658%   $237.3643   $237.36   $237.35   $237.40  
  Purchase #3 $59.39   11.809%   $66.4034   $66.40   $66.40   $66.40  
  Purchase #4 $30.64   10.325%   $33.8036   $33.80   $33.80   $33.80  
  Purchase #5 $207.40   5.718%   $219.2591   $219.26   $219.25   $219.30  
  Purchase #6 $165.37   11.250%   $183.9741   $183.97   $183.95   $184.00  
  Purchase #7 $246.45   8.435%   $267.2381   $267.24   $267.25   $267.20  
  7 purchase totals = $1,132.77       $1,218.7533   $1,218.74   $1,218.70   $1,218.80