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 $217.35   9.816%   $238.6851   $238.69   $238.70   $238.70  
  Purchase #2 $248.86   11.530%   $277.5536   $277.55   $277.55   $277.60  
  Purchase #3 $110.57   13.579%   $125.5843   $125.58   $125.60   $125.60  
  Purchase #4 $236.94   12.551%   $266.6783   $266.68   $266.70   $266.70  
  Purchase #5 $118.60   11.314%   $132.0184   $132.02   $132.00   $132.00  
  Purchase #6 $82.91   11.209%   $92.2034   $92.20   $92.20   $92.20  
  Purchase #7 $135.47   4.201%   $141.1611   $141.16   $141.15   $141.20  
  7 purchase totals = $1,150.70       $1,273.8842   $1,273.88   $1,273.90   $1,274.00