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 $114.73   7.211%   $123.0032   $123.00   $123.00   $123.00  
  Purchase #2 $23.61   3.238%   $24.3745   $24.37   $24.35   $24.40  
  Purchase #3 $61.27   5.639%   $64.725   $64.73   $64.75   $64.70  
  Purchase #4 $195.42   9.277%   $213.5491   $213.55   $213.55   $213.50  
  Purchase #5 $187.75   13.192%   $212.518   $212.52   $212.50   $212.50  
  Purchase #6 $136.66   9.770%   $150.0117   $150.01   $150.00   $150.00  
  Purchase #7 $148.48   11.851%   $166.0764   $166.08   $166.10   $166.10  
  7 purchase totals = $867.92       $954.2579   $954.26   $954.25   $954.20