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 $225.66   5.146%   $237.2725   $237.27   $237.25   $237.30  
  Purchase #2 $185.36   8.196%   $200.5521   $200.55   $200.55   $200.60  
  Purchase #3 $179.53   8.187%   $194.2281   $194.23   $194.25   $194.20  
  Purchase #4 $75.34   5.342%   $79.3647   $79.36   $79.35   $79.40  
  Purchase #5 $23.59   3.437%   $24.4008   $24.40   $24.40   $24.40  
  Purchase #6 $7.64   11.142%   $8.4912   $8.49   $8.50   $8.50  
  Purchase #7 $212.58   11.815%   $237.6963   $237.70   $237.70   $237.70  
  7 purchase totals = $909.70       $982.0057   $982.00   $982.00   $982.10