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 $247.41   6.711%   $264.0137   $264.01   $264.00   $264.00  
  Purchase #2 $223.34   3.408%   $230.9514   $230.95   $230.95   $231.00  
  Purchase #3 $248.88   4.437%   $259.9228   $259.92   $259.90   $259.90  
  Purchase #4 $88.84   4.245%   $92.6113   $92.61   $92.60   $92.60  
  Purchase #5 $25.38   9.275%   $27.734   $27.73   $27.75   $27.70  
  Purchase #6 $39.79   9.565%   $43.5959   $43.60   $43.60   $43.60  
  Purchase #7 $37.97   4.530%   $39.69   $39.69   $39.70   $39.70  
  7 purchase totals = $911.61       $958.5191   $958.51   $958.50   $958.50