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 $205.97   9.236%   $224.9934   $224.99   $225.00   $225.00  
  Purchase #2 $186.58   6.795%   $199.2581   $199.26   $199.25   $199.30  
  Purchase #3 $89.72   6.123%   $95.2136   $95.21   $95.20   $95.20  
  Purchase #4 $71.82   13.758%   $81.701   $81.70   $81.70   $81.70  
  Purchase #5 $112.33   11.762%   $125.5423   $125.54   $125.55   $125.50  
  Purchase #6 $90.34   7.774%   $97.363   $97.36   $97.35   $97.40  
  Purchase #7 $124.93   9.240%   $136.4735   $136.47   $136.45   $136.50  
  7 purchase totals = $881.69       $960.5449   $960.53   $960.50   $960.60