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 $93.82   6.152%   $99.5918   $99.59   $99.60   $99.60  
  Purchase #2 $123.41   3.489%   $127.7158   $127.72   $127.70   $127.70  
  Purchase #3 $104.78   9.830%   $115.0799   $115.08   $115.10   $115.10  
  Purchase #4 $163.36   6.284%   $173.6255   $173.63   $173.65   $173.60  
  Purchase #5 $238.82   12.399%   $268.4313   $268.43   $268.45   $268.40  
  Purchase #6 $58.81   9.275%   $64.2646   $64.26   $64.25   $64.30  
  Purchase #7 $21.28   12.830%   $24.0102   $24.01   $24.00   $24.00  
  7 purchase totals = $804.28       $872.7191   $872.72   $872.75   $872.70