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 $55.47   6.271%   $58.9485   $58.95   $58.95   $58.90  
  Purchase #2 $15.93   8.553%   $17.2925   $17.29   $17.30   $17.30  
  Purchase #3 $142.66   11.206%   $158.6465   $158.65   $158.65   $158.60  
  Purchase #4 $89.36   5.678%   $94.4339   $94.43   $94.45   $94.40  
  Purchase #5 $186.53   11.378%   $207.7534   $207.75   $207.75   $207.80  
  Purchase #6 $60.30   12.139%   $67.6198   $67.62   $67.60   $67.60  
  Purchase #7 $156.60   6.276%   $166.4282   $166.43   $166.45   $166.40  
  7 purchase totals = $706.85       $771.1228   $771.12   $771.15   $771.00