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 $60.55   4.497%   $63.2729   $63.27   $63.25   $63.30  
  Purchase #2 $44.71   3.612%   $46.3249   $46.32   $46.30   $46.30  
  Purchase #3 $120.65   11.260%   $134.2352   $134.24   $134.25   $134.20  
  Purchase #4 $111.77   7.833%   $120.5249   $120.52   $120.50   $120.50  
  Purchase #5 $123.77   6.672%   $132.0279   $132.03   $132.05   $132.00  
  Purchase #6 $238.27   7.582%   $256.3356   $256.34   $256.35   $256.30  
  Purchase #7 $101.38   9.389%   $110.8986   $110.90   $110.90   $110.90  
  7 purchase totals = $801.10       $863.6200   $863.62   $863.60   $863.50