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 $221.59   8.746%   $240.9703   $240.97   $240.95   $241.00  
  Purchase #2 $57.51   10.416%   $63.5002   $63.50   $63.50   $63.50  
  Purchase #3 $237.41   8.804%   $258.3116   $258.31   $258.30   $258.30  
  Purchase #4 $156.81   8.834%   $170.6626   $170.66   $170.65   $170.70  
  Purchase #5 $135.58   11.515%   $151.192   $151.19   $151.20   $151.20  
  Purchase #6 $250.32   12.766%   $282.2759   $282.28   $282.30   $282.30  
  Purchase #7 $123.40   7.367%   $132.4909   $132.49   $132.50   $132.50  
  7 purchase totals = $1,182.62       $1,299.4035   $1,299.40   $1,299.40   $1,299.50