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 $62.97   6.353%   $66.9705   $66.97   $66.95   $67.00  
  Purchase #2 $30.65   4.716%   $32.0955   $32.10   $32.10   $32.10  
  Purchase #3 $27.25   6.782%   $29.0981   $29.10   $29.10   $29.10  
  Purchase #4 $53.57   7.140%   $57.3949   $57.39   $57.40   $57.40  
  Purchase #5 $234.71   13.446%   $266.2691   $266.27   $266.25   $266.30  
  Purchase #6 $96.94   13.227%   $109.7623   $109.76   $109.75   $109.80  
  Purchase #7 $144.34   12.241%   $162.0087   $162.01   $162.00   $162.00  
  7 purchase totals = $650.43       $723.5991   $723.60   $723.55   $723.70