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 $82.95   12.869%   $93.6248   $93.62   $93.60   $93.60  
  Purchase #2 $161.95   9.301%   $177.013   $177.01   $177.00   $177.00  
  Purchase #3 $104.85   10.316%   $115.6663   $115.67   $115.65   $115.70  
  Purchase #4 $193.92   9.824%   $212.9707   $212.97   $212.95   $213.00  
  Purchase #5 $241.88   12.338%   $271.7232   $271.72   $271.70   $271.70  
  Purchase #6 $130.46   13.697%   $148.3291   $148.33   $148.35   $148.30  
  Purchase #7 $101.93   13.483%   $115.6732   $115.67   $115.65   $115.70  
  7 purchase totals = $1,017.94       $1,135.0003   $1,134.99   $1,134.90   $1,135.00