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 $62.77   5.165%   $66.0121   $66.01   $66.00   $66.00  
  Purchase #2 $218.89   10.494%   $241.8603   $241.86   $241.85   $241.90  
  Purchase #3 $223.29   13.762%   $254.0192   $254.02   $254.00   $254.00  
  Purchase #4 $143.38   11.370%   $159.6823   $159.68   $159.70   $159.70  
  Purchase #5 $189.26   13.830%   $215.4347   $215.43   $215.45   $215.40  
  Purchase #6 $232.77   5.664%   $245.9541   $245.95   $245.95   $246.00  
  Purchase #7 $245.39   7.741%   $264.3856   $264.39   $264.40   $264.40  
  7 purchase totals = $1,315.75       $1,447.3483   $1,447.34   $1,447.35   $1,447.40