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 $237.44   6.360%   $252.5412   $252.54   $252.55   $252.50  
  Purchase #2 $224.60   11.802%   $251.1073   $251.11   $251.10   $251.10  
  Purchase #3 $86.33   10.755%   $95.6148   $95.61   $95.60   $95.60  
  Purchase #4 $165.56   10.406%   $182.7882   $182.79   $182.80   $182.80  
  Purchase #5 $60.30   3.142%   $62.1946   $62.19   $62.20   $62.20  
  Purchase #6 $78.40   8.598%   $85.1408   $85.14   $85.15   $85.10  
  Purchase #7 $125.29   4.835%   $131.3478   $131.35   $131.35   $131.30  
  7 purchase totals = $977.92       $1,060.7347   $1,060.73   $1,060.75   $1,060.60