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 $92.43   12.415%   $103.9052   $103.91   $103.90   $103.90  
  Purchase #2 $36.90   4.492%   $38.5575   $38.56   $38.55   $38.60  
  Purchase #3 $65.74   5.556%   $69.3925   $69.39   $69.40   $69.40  
  Purchase #4 $167.49   5.596%   $176.8627   $176.86   $176.85   $176.90  
  Purchase #5 $204.64   9.121%   $223.3052   $223.31   $223.30   $223.30  
  Purchase #6 $5.71   5.678%   $6.0342   $6.03   $6.05   $6.00  
  Purchase #7 $221.69   12.639%   $249.7094   $249.71   $249.70   $249.70  
  7 purchase totals = $794.60       $867.7667   $867.77   $867.75   $867.80