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 $53.32   13.788%   $60.6718   $60.67   $60.65   $60.70  
  Purchase #2 $121.52   8.415%   $131.7459   $131.75   $131.75   $131.70  
  Purchase #3 $49.53   7.590%   $53.2893   $53.29   $53.30   $53.30  
  Purchase #4 $20.83   11.634%   $23.2534   $23.25   $23.25   $23.30  
  Purchase #5 $224.85   9.822%   $246.9348   $246.93   $246.95   $246.90  
  Purchase #6 $91.87   5.207%   $96.6537   $96.65   $96.65   $96.70  
  Purchase #7 $60.87   4.706%   $63.7345   $63.73   $63.75   $63.70  
  7 purchase totals = $622.79       $676.2834   $676.27   $676.30   $676.30