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 $73.90   4.169%   $76.9809   $76.98   $77.00   $77.00  
  Purchase #2 $128.46   12.854%   $144.9722   $144.97   $144.95   $145.00  
  Purchase #3 $143.83   12.291%   $161.5081   $161.51   $161.50   $161.50  
  Purchase #4 $195.55   6.350%   $207.9674   $207.97   $207.95   $208.00  
  Purchase #5 $228.96   13.536%   $259.952   $259.95   $259.95   $260.00  
  Purchase #6 $69.34   12.869%   $78.2634   $78.26   $78.25   $78.30  
  Purchase #7 $96.90   7.822%   $104.4795   $104.48   $104.50   $104.50  
  7 purchase totals = $936.94       $1,034.1235   $1,034.12   $1,034.10   $1,034.30