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 $178.45   13.195%   $201.9965   $202.00   $202.00   $202.00  
  Purchase #2 $96.99   8.826%   $105.5503   $105.55   $105.55   $105.60  
  Purchase #3 $174.42   4.207%   $181.7578   $181.76   $181.75   $181.80  
  Purchase #4 $53.26   5.539%   $56.2101   $56.21   $56.20   $56.20  
  Purchase #5 $154.53   3.343%   $159.6959   $159.70   $159.70   $159.70  
  Purchase #6 $8.73   4.265%   $9.1023   $9.10   $9.10   $9.10  
  Purchase #7 $214.66   10.519%   $237.2401   $237.24   $237.25   $237.20  
  7 purchase totals = $881.04       $951.5530   $951.56   $951.55   $951.60