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 $229.95   4.852%   $241.1072   $241.11   $241.10   $241.10  
  Purchase #2 $50.86   7.103%   $54.4726   $54.47   $54.45   $54.50  
  Purchase #3 $199.90   13.236%   $226.3588   $226.36   $226.35   $226.40  
  Purchase #4 $80.44   3.772%   $83.4742   $83.47   $83.45   $83.50  
  Purchase #5 $241.71   11.182%   $268.738   $268.74   $268.75   $268.70  
  Purchase #6 $70.25   9.520%   $76.9378   $76.94   $76.95   $76.90  
  Purchase #7 $150.46   12.329%   $169.0102   $169.01   $169.00   $169.00  
  7 purchase totals = $1,023.57       $1,120.0988   $1,120.10   $1,120.05   $1,120.10