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 $189.89   11.223%   $211.2014   $211.20   $211.20   $211.20  
  Purchase #2 $127.45   9.299%   $139.3016   $139.30   $139.30   $139.30  
  Purchase #3 $82.47   4.352%   $86.0591   $86.06   $86.05   $86.10  
  Purchase #4 $44.77   10.849%   $49.6271   $49.63   $49.65   $49.60  
  Purchase #5 $166.54   8.202%   $180.1996   $180.20   $180.20   $180.20  
  Purchase #6 $238.86   4.840%   $250.4208   $250.42   $250.40   $250.40  
  Purchase #7 $64.90   3.271%   $67.0229   $67.02   $67.00   $67.00  
  7 purchase totals = $914.88       $983.8325   $983.83   $983.80   $983.80