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 $201.39   8.534%   $218.5766   $218.58   $218.60   $218.60  
  Purchase #2 $60.87   12.590%   $68.5335   $68.53   $68.55   $68.50  
  Purchase #3 $165.84   10.193%   $182.7441   $182.74   $182.75   $182.70  
  Purchase #4 $50.43   13.451%   $57.2133   $57.21   $57.20   $57.20  
  Purchase #5 $191.98   7.245%   $205.889   $205.89   $205.90   $205.90  
  Purchase #6 $15.97   11.370%   $17.7858   $17.79   $17.80   $17.80  
  Purchase #7 $190.47   12.246%   $213.795   $213.80   $213.80   $213.80  
  7 purchase totals = $876.95       $964.5373   $964.54   $964.60   $964.50