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 $162.65   13.555%   $184.6972   $184.70   $184.70   $184.70  
  Purchase #2 $118.93   11.864%   $133.0399   $133.04   $133.05   $133.00  
  Purchase #3 $70.75   6.399%   $75.2773   $75.28   $75.30   $75.30  
  Purchase #4 $242.32   13.534%   $275.1156   $275.12   $275.10   $275.10  
  Purchase #5 $8.39   13.618%   $9.5326   $9.53   $9.55   $9.50  
  Purchase #6 $88.78   9.419%   $97.1422   $97.14   $97.15   $97.10  
  Purchase #7 $242.25   3.690%   $251.189   $251.19   $251.20   $251.20  
  7 purchase totals = $934.07       $1,025.9938   $1,026.00   $1,026.05   $1,025.90