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 $63.94   3.505%   $66.1811   $66.18   $66.20   $66.20  
  Purchase #2 $94.60   12.429%   $106.3578   $106.36   $106.35   $106.40  
  Purchase #3 $154.75   10.316%   $170.714   $170.71   $170.70   $170.70  
  Purchase #4 $83.84   9.774%   $92.0345   $92.03   $92.05   $92.00  
  Purchase #5 $38.94   13.715%   $44.2806   $44.28   $44.30   $44.30  
  Purchase #6 $29.44   13.335%   $33.3658   $33.37   $33.35   $33.40  
  Purchase #7 $235.94   9.659%   $258.7294   $258.73   $258.75   $258.70  
  7 purchase totals = $701.45       $771.6632   $771.66   $771.70   $771.70