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 $22.51   4.771%   $23.584   $23.58   $23.60   $23.60  
  Purchase #2 $34.45   4.211%   $35.9007   $35.90   $35.90   $35.90  
  Purchase #3 $235.61   5.723%   $249.094   $249.09   $249.10   $249.10  
  Purchase #4 $47.64   5.651%   $50.3321   $50.33   $50.35   $50.30  
  Purchase #5 $201.37   4.781%   $210.9975   $211.00   $211.00   $211.00  
  Purchase #6 $71.84   6.538%   $76.5369   $76.54   $76.55   $76.50  
  Purchase #7 $138.87   11.508%   $154.8512   $154.85   $154.85   $154.90  
  7 purchase totals = $752.29       $801.2964   $801.29   $801.35   $801.30