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 $62.95   13.350%   $71.3538   $71.35   $71.35   $71.40  
  Purchase #2 $71.74   13.726%   $81.587   $81.59   $81.60   $81.60  
  Purchase #3 $124.89   4.256%   $130.2053   $130.21   $130.20   $130.20  
  Purchase #4 $87.84   11.221%   $97.6965   $97.70   $97.70   $97.70  
  Purchase #5 $11.65   8.400%   $12.6286   $12.63   $12.65   $12.60  
  Purchase #6 $231.70   12.390%   $260.4076   $260.41   $260.40   $260.40  
  Purchase #7 $36.54   3.426%   $37.7919   $37.79   $37.80   $37.80  
  7 purchase totals = $627.31       $691.6707   $691.68   $691.70   $691.70