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 $206.99   4.255%   $215.7974   $215.80   $215.80   $215.80  
  Purchase #2 $110.41   6.131%   $117.1792   $117.18   $117.20   $117.20  
  Purchase #3 $58.27   6.855%   $62.2644   $62.26   $62.25   $62.30  
  Purchase #4 $224.66   12.665%   $253.1132   $253.11   $253.10   $253.10  
  Purchase #5 $71.42   6.313%   $75.9287   $75.93   $75.95   $75.90  
  Purchase #6 $68.33   3.589%   $70.7824   $70.78   $70.80   $70.80  
  Purchase #7 $183.95   13.205%   $208.2406   $208.24   $208.25   $208.20  
  7 purchase totals = $924.03       $1,003.3059   $1,003.30   $1,003.35   $1,003.30