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 $69.76   8.791%   $75.8926   $75.89   $75.90   $75.90  
  Purchase #2 $89.44   8.518%   $97.0585   $97.06   $97.05   $97.10  
  Purchase #3 $23.64   10.841%   $26.2028   $26.20   $26.20   $26.20  
  Purchase #4 $93.89   5.170%   $98.7441   $98.74   $98.75   $98.70  
  Purchase #5 $116.98   5.469%   $123.3776   $123.38   $123.40   $123.40  
  Purchase #6 $213.74   12.204%   $239.8248   $239.82   $239.80   $239.80  
  Purchase #7 $198.56   5.708%   $209.8938   $209.89   $209.90   $209.90  
  7 purchase totals = $806.01       $870.9942   $870.98   $871.00   $871.00