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 $39.94   7.715%   $43.0214   $43.02   $43.00   $43.00  
  Purchase #2 $220.26   8.346%   $238.6429   $238.64   $238.65   $238.60  
  Purchase #3 $34.80   5.566%   $36.737   $36.74   $36.75   $36.70  
  Purchase #4 $125.65   4.531%   $131.3432   $131.34   $131.35   $131.30  
  Purchase #5 $60.95   7.583%   $65.5718   $65.57   $65.55   $65.60  
  Purchase #6 $214.33   13.312%   $242.8616   $242.86   $242.85   $242.90  
  Purchase #7 $188.54   4.293%   $196.634   $196.63   $196.65   $196.60  
  7 purchase totals = $884.47       $954.8119   $954.80   $954.80   $954.70