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 $60.49   5.238%   $63.6585   $63.66   $63.65   $63.70  
  Purchase #2 $96.87   9.776%   $106.34   $106.34   $106.35   $106.30  
  Purchase #3 $54.58   13.474%   $61.9341   $61.93   $61.95   $61.90  
  Purchase #4 $55.87   5.770%   $59.0937   $59.09   $59.10   $59.10  
  Purchase #5 $92.47   3.530%   $95.7342   $95.73   $95.75   $95.70  
  Purchase #6 $244.61   13.511%   $277.6593   $277.66   $277.65   $277.70  
  Purchase #7 $8.86   10.113%   $9.756   $9.76   $9.75   $9.80  
  7 purchase totals = $613.75       $674.1758   $674.17   $674.20   $674.20