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 $244.58   12.622%   $275.4509   $275.45   $275.45   $275.50  
  Purchase #2 $186.96   5.234%   $196.7455   $196.75   $196.75   $196.70  
  Purchase #3 $206.70   8.365%   $223.9905   $223.99   $224.00   $224.00  
  Purchase #4 $186.92   8.390%   $202.6026   $202.60   $202.60   $202.60  
  Purchase #5 $77.73   5.256%   $81.8155   $81.82   $81.80   $81.80  
  Purchase #6 $184.27   5.674%   $194.7255   $194.73   $194.75   $194.70  
  Purchase #7 $159.92   8.566%   $173.6187   $173.62   $173.60   $173.60  
  7 purchase totals = $1,247.08       $1,348.9492   $1,348.96   $1,348.95   $1,348.90