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 $245.62   7.348%   $263.6682   $263.67   $263.65   $263.70  
  Purchase #2 $95.82   8.855%   $104.3049   $104.30   $104.30   $104.30  
  Purchase #3 $155.70   9.317%   $170.2066   $170.21   $170.20   $170.20  
  Purchase #4 $94.56   3.282%   $97.6635   $97.66   $97.65   $97.70  
  Purchase #5 $75.85   5.202%   $79.7957   $79.80   $79.80   $79.80  
  Purchase #6 $132.53   6.282%   $140.8555   $140.86   $140.85   $140.90  
  Purchase #7 $194.74   3.208%   $200.9873   $200.99   $201.00   $201.00  
  7 purchase totals = $994.82       $1,057.4817   $1,057.49   $1,057.45   $1,057.60