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 $217.87   12.236%   $244.5286   $244.53   $244.55   $244.50  
  Purchase #2 $172.43   12.516%   $194.0113   $194.01   $194.00   $194.00  
  Purchase #3 $81.80   6.222%   $86.8896   $86.89   $86.90   $86.90  
  Purchase #4 $56.42   12.525%   $63.4866   $63.49   $63.50   $63.50  
  Purchase #5 $68.25   5.770%   $72.188   $72.19   $72.20   $72.20  
  Purchase #6 $202.58   6.803%   $216.3615   $216.36   $216.35   $216.40  
  Purchase #7 $70.64   4.516%   $73.8301   $73.83   $73.85   $73.80  
  7 purchase totals = $869.99       $951.2957   $951.30   $951.35   $951.30