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 $84.66   13.726%   $96.2804   $96.28   $96.30   $96.30  
  Purchase #2 $227.39   3.793%   $236.0149   $236.01   $236.00   $236.00  
  Purchase #3 $37.63   4.573%   $39.3508   $39.35   $39.35   $39.40  
  Purchase #4 $206.65   11.534%   $230.485   $230.49   $230.50   $230.50  
  Purchase #5 $62.99   8.785%   $68.5237   $68.52   $68.50   $68.50  
  Purchase #6 $143.87   8.631%   $156.2874   $156.29   $156.30   $156.30  
  Purchase #7 $175.98   11.863%   $196.8565   $196.86   $196.85   $196.90  
  7 purchase totals = $939.17       $1,023.7987   $1,023.80   $1,023.80   $1,023.90