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 $238.45   6.203%   $253.2411   $253.24   $253.25   $253.20  
  Purchase #2 $12.27   6.337%   $13.0475   $13.05   $13.05   $13.00  
  Purchase #3 $157.60   12.399%   $177.1408   $177.14   $177.15   $177.10  
  Purchase #4 $215.59   9.160%   $235.338   $235.34   $235.35   $235.30  
  Purchase #5 $234.48   9.305%   $256.2984   $256.30   $256.30   $256.30  
  Purchase #6 $68.33   8.265%   $73.9775   $73.98   $74.00   $74.00  
  Purchase #7 $64.57   4.549%   $67.5073   $67.51   $67.50   $67.50  
  7 purchase totals = $991.29       $1,076.5506   $1,076.56   $1,076.60   $1,076.40