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 $194.88   11.689%   $217.6595   $217.66   $217.65   $217.70  
  Purchase #2 $44.87   9.396%   $49.086   $49.09   $49.10   $49.10  
  Purchase #3 $182.77   6.413%   $194.491   $194.49   $194.50   $194.50  
  Purchase #4 $58.67   3.821%   $60.9118   $60.91   $60.90   $60.90  
  Purchase #5 $217.81   12.446%   $244.9186   $244.92   $244.90   $244.90  
  Purchase #6 $148.78   7.342%   $159.7034   $159.70   $159.70   $159.70  
  Purchase #7 $238.27   11.693%   $266.1309   $266.13   $266.15   $266.10  
  7 purchase totals = $1,086.05       $1,192.9012   $1,192.90   $1,192.90   $1,192.90