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 $84.48   9.195%   $92.2479   $92.25   $92.25   $92.20  
  Purchase #2 $44.71   6.686%   $47.6993   $47.70   $47.70   $47.70  
  Purchase #3 $71.54   4.710%   $74.9095   $74.91   $74.90   $74.90  
  Purchase #4 $57.75   8.344%   $62.5687   $62.57   $62.55   $62.60  
  Purchase #5 $201.34   3.803%   $208.997   $209.00   $209.00   $209.00  
  Purchase #6 $172.85   5.432%   $182.2392   $182.24   $182.25   $182.20  
  Purchase #7 $121.74   13.628%   $138.3307   $138.33   $138.35   $138.30  
  7 purchase totals = $754.41       $806.9923   $807.00   $807.00   $806.90