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 $217.74   12.373%   $244.681   $244.68   $244.70   $244.70  
  Purchase #2 $48.70   3.567%   $50.4371   $50.44   $50.45   $50.40  
  Purchase #3 $174.98   10.761%   $193.8096   $193.81   $193.80   $193.80  
  Purchase #4 $113.94   9.763%   $125.064   $125.06   $125.05   $125.10  
  Purchase #5 $58.57   12.293%   $65.77   $65.77   $65.75   $65.80  
  Purchase #6 $202.86   10.616%   $224.3956   $224.40   $224.40   $224.40  
  Purchase #7 $233.55   5.672%   $246.797   $246.80   $246.80   $246.80  
  7 purchase totals = $1,050.34       $1,150.9543   $1,150.96   $1,150.95   $1,151.00