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 $92.79   5.269%   $97.6791   $97.68   $97.70   $97.70  
  Purchase #2 $135.79   12.833%   $153.2159   $153.22   $153.20   $153.20  
  Purchase #3 $180.76   6.393%   $192.316   $192.32   $192.30   $192.30  
  Purchase #4 $75.48   7.717%   $81.3048   $81.30   $81.30   $81.30  
  Purchase #5 $95.30   11.738%   $106.4863   $106.49   $106.50   $106.50  
  Purchase #6 $135.74   3.296%   $140.214   $140.21   $140.20   $140.20  
  Purchase #7 $143.62   13.213%   $162.5965   $162.60   $162.60   $162.60  
  7 purchase totals = $859.48       $933.8126   $933.82   $933.80   $933.80