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 $78.61   6.550%   $83.759   $83.76   $83.75   $83.80  
  Purchase #2 $244.66   7.697%   $263.4915   $263.49   $263.50   $263.50  
  Purchase #3 $54.67   7.523%   $58.7828   $58.78   $58.80   $58.80  
  Purchase #4 $74.87   9.359%   $81.8771   $81.88   $81.90   $81.90  
  Purchase #5 $69.26   10.198%   $76.3231   $76.32   $76.30   $76.30  
  Purchase #6 $227.45   8.729%   $247.3041   $247.30   $247.30   $247.30  
  Purchase #7 $68.84   10.670%   $76.1852   $76.19   $76.20   $76.20  
  7 purchase totals = $818.36       $887.7228   $887.72   $887.75   $887.80