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 $195.43   6.262%   $207.6678   $207.67   $207.65   $207.70  
  Purchase #2 $58.79   12.442%   $66.1047   $66.10   $66.10   $66.10  
  Purchase #3 $85.48   11.399%   $95.2239   $95.22   $95.20   $95.20  
  Purchase #4 $96.57   9.720%   $105.9566   $105.96   $105.95   $106.00  
  Purchase #5 $55.91   6.711%   $59.6621   $59.66   $59.65   $59.70  
  Purchase #6 $140.56   10.173%   $154.8592   $154.86   $154.85   $154.90  
  Purchase #7 $250.52   9.771%   $274.9983   $275.00   $275.00   $275.00  
  7 purchase totals = $883.26       $964.4726   $964.47   $964.40   $964.60