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 $241.37   7.706%   $259.97   $259.97   $259.95   $260.00  
  Purchase #2 $106.60   6.413%   $113.4363   $113.44   $113.45   $113.40  
  Purchase #3 $199.38   8.191%   $215.7112   $215.71   $215.70   $215.70  
  Purchase #4 $63.53   4.475%   $66.373   $66.37   $66.35   $66.40  
  Purchase #5 $186.56   4.416%   $194.7985   $194.80   $194.80   $194.80  
  Purchase #6 $250.94   12.376%   $281.9963   $282.00   $282.00   $282.00  
  Purchase #7 $58.79   8.810%   $63.9694   $63.97   $63.95   $64.00  
  7 purchase totals = $1,107.17       $1,196.2547   $1,196.26   $1,196.20   $1,196.30