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 $90.73   4.674%   $94.9707   $94.97   $94.95   $95.00  
  Purchase #2 $209.96   9.825%   $230.5886   $230.59   $230.60   $230.60  
  Purchase #3 $110.36   6.459%   $117.4882   $117.49   $117.50   $117.50  
  Purchase #4 $84.45   6.600%   $90.0237   $90.02   $90.00   $90.00  
  Purchase #5 $54.46   7.692%   $58.6491   $58.65   $58.65   $58.60  
  Purchase #6 $84.62   4.725%   $88.6183   $88.62   $88.60   $88.60  
  Purchase #7 $111.94   9.630%   $122.7198   $122.72   $122.70   $122.70  
  7 purchase totals = $746.52       $803.0584   $803.06   $803.00   $803.00