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 $50.68   11.464%   $56.49   $56.49   $56.50   $56.50  
  Purchase #2 $196.49   11.122%   $218.3436   $218.34   $218.35   $218.30  
  Purchase #3 $98.68   4.666%   $103.2844   $103.28   $103.30   $103.30  
  Purchase #4 $61.42   13.645%   $69.8008   $69.80   $69.80   $69.80  
  Purchase #5 $221.71   8.135%   $239.7461   $239.75   $239.75   $239.70  
  Purchase #6 $53.61   4.519%   $56.0326   $56.03   $56.05   $56.00  
  Purchase #7 $140.72   8.145%   $152.1816   $152.18   $152.20   $152.20  
  7 purchase totals = $823.31       $895.8791   $895.87   $895.95   $895.80