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 $244.82   12.241%   $274.7884   $274.79   $274.80   $274.80  
  Purchase #2 $172.43   10.159%   $189.9472   $189.95   $189.95   $189.90  
  Purchase #3 $92.57   4.306%   $96.5561   $96.56   $96.55   $96.60  
  Purchase #4 $217.86   4.541%   $227.753   $227.75   $227.75   $227.80  
  Purchase #5 $119.60   5.704%   $126.422   $126.42   $126.40   $126.40  
  Purchase #6 $144.53   3.150%   $149.0827   $149.08   $149.10   $149.10  
  Purchase #7 $132.39   3.527%   $137.0594   $137.06   $137.05   $137.10  
  7 purchase totals = $1,124.20       $1,201.6088   $1,201.61   $1,201.60   $1,201.70