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 $216.50   11.573%   $241.5555   $241.56   $241.55   $241.60  
  Purchase #2 $224.67   8.739%   $244.3039   $244.30   $244.30   $244.30  
  Purchase #3 $108.85   10.800%   $120.6058   $120.61   $120.60   $120.60  
  Purchase #4 $100.88   8.625%   $109.5809   $109.58   $109.60   $109.60  
  Purchase #5 $215.40   3.404%   $222.7322   $222.73   $222.75   $222.70  
  Purchase #6 $110.79   8.209%   $119.8848   $119.88   $119.90   $119.90  
  Purchase #7 $236.32   12.692%   $266.3137   $266.31   $266.30   $266.30  
  7 purchase totals = $1,213.41       $1,324.9768   $1,324.97   $1,325.00   $1,325.00