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 $218.49   10.459%   $241.3419   $241.34   $241.35   $241.30  
  Purchase #2 $84.91   11.624%   $94.7799   $94.78   $94.80   $94.80  
  Purchase #3 $39.89   10.316%   $44.0051   $44.01   $44.00   $44.00  
  Purchase #4 $218.73   11.522%   $243.9321   $243.93   $243.95   $243.90  
  Purchase #5 $11.76   6.318%   $12.503   $12.50   $12.50   $12.50  
  Purchase #6 $47.43   13.381%   $53.7766   $53.78   $53.80   $53.80  
  Purchase #7 $216.25   8.531%   $234.6983   $234.70   $234.70   $234.70  
  7 purchase totals = $837.46       $925.0369   $925.04   $925.10   $925.00