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 $96.25   6.559%   $102.563   $102.56   $102.55   $102.60  
  Purchase #2 $117.57   6.805%   $125.5706   $125.57   $125.55   $125.60  
  Purchase #3 $228.82   9.478%   $250.5076   $250.51   $250.50   $250.50  
  Purchase #4 $91.25   6.204%   $96.9112   $96.91   $96.90   $96.90  
  Purchase #5 $67.31   13.611%   $76.4716   $76.47   $76.45   $76.50  
  Purchase #6 $65.53   9.342%   $71.6518   $71.65   $71.65   $71.70  
  Purchase #7 $74.66   9.451%   $81.7161   $81.72   $81.70   $81.70  
  7 purchase totals = $741.39       $805.3919   $805.39   $805.30   $805.50