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 $89.76   5.538%   $94.7309   $94.73   $94.75   $94.70  
  Purchase #2 $201.26   4.268%   $209.8498   $209.85   $209.85   $209.80  
  Purchase #3 $127.78   5.748%   $135.1248   $135.12   $135.10   $135.10  
  Purchase #4 $65.60   7.723%   $70.6663   $70.67   $70.65   $70.70  
  Purchase #5 $190.99   10.427%   $210.9045   $210.90   $210.90   $210.90  
  Purchase #6 $16.59   3.212%   $17.1229   $17.12   $17.10   $17.10  
  Purchase #7 $108.62   7.574%   $116.8469   $116.85   $116.85   $116.80  
  7 purchase totals = $800.60       $855.2461   $855.24   $855.20   $855.10