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 $68.97   8.625%   $74.9187   $74.92   $74.90   $74.90  
  Purchase #2 $164.96   4.710%   $172.7296   $172.73   $172.75   $172.70  
  Purchase #3 $250.49   6.726%   $267.338   $267.34   $267.35   $267.30  
  Purchase #4 $64.78   13.366%   $73.4385   $73.44   $73.45   $73.40  
  Purchase #5 $44.50   13.809%   $50.645   $50.65   $50.65   $50.60  
  Purchase #6 $68.56   10.574%   $75.8095   $75.81   $75.80   $75.80  
  Purchase #7 $32.50   12.801%   $36.6603   $36.66   $36.65   $36.70  
  7 purchase totals = $694.76       $751.5396   $751.55   $751.55   $751.40