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 $232.87   9.201%   $254.2964   $254.30   $254.30   $254.30  
  Purchase #2 $188.65   8.639%   $204.9475   $204.95   $204.95   $204.90  
  Purchase #3 $32.90   12.312%   $36.9506   $36.95   $36.95   $37.00  
  Purchase #4 $5.86   3.277%   $6.052   $6.05   $6.05   $6.10  
  Purchase #5 $24.93   6.783%   $26.621   $26.62   $26.60   $26.60  
  Purchase #6 $7.95   6.150%   $8.4389   $8.44   $8.45   $8.40  
  Purchase #7 $108.55   7.798%   $117.0147   $117.01   $117.00   $117.00  
  7 purchase totals = $601.71       $654.3211   $654.32   $654.30   $654.30