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 $235.41   10.717%   $260.6389   $260.64   $260.65   $260.60  
  Purchase #2 $100.37   3.810%   $104.1941   $104.19   $104.20   $104.20  
  Purchase #3 $125.58   4.416%   $131.1256   $131.13   $131.15   $131.10  
  Purchase #4 $164.79   9.145%   $179.86   $179.86   $179.85   $179.90  
  Purchase #5 $205.40   6.102%   $217.9335   $217.93   $217.95   $217.90  
  Purchase #6 $46.37   8.581%   $50.349   $50.35   $50.35   $50.30  
  Purchase #7 $185.31   11.744%   $207.0728   $207.07   $207.05   $207.10  
  7 purchase totals = $1,063.23       $1,151.1739   $1,151.17   $1,151.20   $1,151.10