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 $119.87   4.730%   $125.5399   $125.54   $125.55   $125.50  
  Purchase #2 $168.27   13.651%   $191.2405   $191.24   $191.25   $191.20  
  Purchase #3 $141.55   13.301%   $160.3776   $160.38   $160.40   $160.40  
  Purchase #4 $119.62   11.102%   $132.9002   $132.90   $132.90   $132.90  
  Purchase #5 $123.84   10.357%   $136.6661   $136.67   $136.65   $136.70  
  Purchase #6 $37.82   13.868%   $43.0649   $43.06   $43.05   $43.10  
  Purchase #7 $128.49   6.774%   $137.1939   $137.19   $137.20   $137.20  
  7 purchase totals = $839.46       $926.9831   $926.98   $927.00   $927.00