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 $236.51   13.664%   $268.8267   $268.83   $268.85   $268.80  
  Purchase #2 $112.32   11.244%   $124.9493   $124.95   $124.95   $124.90  
  Purchase #3 $193.73   3.406%   $200.3284   $200.33   $200.35   $200.30  
  Purchase #4 $225.45   10.575%   $249.2913   $249.29   $249.30   $249.30  
  Purchase #5 $23.48   6.743%   $25.0633   $25.06   $25.05   $25.10  
  Purchase #6 $165.92   4.388%   $173.2006   $173.20   $173.20   $173.20  
  Purchase #7 $108.52   11.227%   $120.7035   $120.70   $120.70   $120.70  
  7 purchase totals = $1,065.93       $1,162.3631   $1,162.36   $1,162.40   $1,162.30