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 $37.32   11.855%   $41.7443   $41.74   $41.75   $41.70  
  Purchase #2 $69.70   8.307%   $75.49   $75.49   $75.50   $75.50  
  Purchase #3 $137.74   3.226%   $142.1835   $142.18   $142.20   $142.20  
  Purchase #4 $212.99   4.160%   $221.8504   $221.85   $221.85   $221.90  
  Purchase #5 $191.81   4.236%   $199.9351   $199.94   $199.95   $199.90  
  Purchase #6 $203.26   9.762%   $223.1022   $223.10   $223.10   $223.10  
  Purchase #7 $57.59   11.717%   $64.3378   $64.34   $64.35   $64.30  
  7 purchase totals = $910.41       $968.6433   $968.64   $968.70   $968.60