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 $215.44   13.160%   $243.7919   $243.79   $243.80   $243.80  
  Purchase #2 $35.70   6.644%   $38.0719   $38.07   $38.05   $38.10  
  Purchase #3 $80.86   6.348%   $85.993   $85.99   $86.00   $86.00  
  Purchase #4 $58.78   13.221%   $66.5513   $66.55   $66.55   $66.60  
  Purchase #5 $215.88   11.772%   $241.2934   $241.29   $241.30   $241.30  
  Purchase #6 $139.99   13.584%   $159.0062   $159.01   $159.00   $159.00  
  Purchase #7 $137.57   6.375%   $146.3401   $146.34   $146.35   $146.30  
  7 purchase totals = $884.22       $981.0478   $981.04   $981.05   $981.10