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 $67.59   12.602%   $76.1077   $76.11   $76.10   $76.10  
  Purchase #2 $200.86   6.586%   $214.0886   $214.09   $214.10   $214.10  
  Purchase #3 $107.46   11.815%   $120.1564   $120.16   $120.15   $120.20  
  Purchase #4 $201.34   11.364%   $224.2203   $224.22   $224.20   $224.20  
  Purchase #5 $30.97   6.515%   $32.9877   $32.99   $33.00   $33.00  
  Purchase #6 $153.72   3.767%   $159.5106   $159.51   $159.50   $159.50  
  Purchase #7 $152.26   4.830%   $159.6142   $159.61   $159.60   $159.60  
  7 purchase totals = $914.20       $986.6855   $986.69   $986.65   $986.70