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 $168.46   4.812%   $176.5663   $176.57   $176.55   $176.60  
  Purchase #2 $235.81   12.869%   $266.1564   $266.16   $266.15   $266.20  
  Purchase #3 $226.66   5.169%   $238.3761   $238.38   $238.40   $238.40  
  Purchase #4 $51.42   11.541%   $57.3544   $57.35   $57.35   $57.40  
  Purchase #5 $161.88   11.241%   $180.0769   $180.08   $180.10   $180.10  
  Purchase #6 $217.42   12.487%   $244.5692   $244.57   $244.55   $244.60  
  Purchase #7 $131.78   4.757%   $138.0488   $138.05   $138.05   $138.00  
  7 purchase totals = $1,193.43       $1,301.1481   $1,301.16   $1,301.15   $1,301.30