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 $85.96   8.437%   $93.2124   $93.21   $93.20   $93.20  
  Purchase #2 $111.95   10.271%   $123.4484   $123.45   $123.45   $123.40  
  Purchase #3 $247.49   11.269%   $275.3796   $275.38   $275.40   $275.40  
  Purchase #4 $224.70   3.330%   $232.1825   $232.18   $232.20   $232.20  
  Purchase #5 $222.80   7.521%   $239.5568   $239.56   $239.55   $239.60  
  Purchase #6 $194.97   8.531%   $211.6029   $211.60   $211.60   $211.60  
  Purchase #7 $156.54   7.417%   $168.1506   $168.15   $168.15   $168.20  
  7 purchase totals = $1,244.41       $1,343.5332   $1,343.53   $1,343.55   $1,343.60