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 $62.42   3.545%   $64.6328   $64.63   $64.65   $64.60  
  Purchase #2 $190.74   13.697%   $216.8657   $216.87   $216.85   $216.90  
  Purchase #3 $13.74   9.753%   $15.0801   $15.08   $15.10   $15.10  
  Purchase #4 $213.29   4.275%   $222.4081   $222.41   $222.40   $222.40  
  Purchase #5 $139.60   6.503%   $148.6782   $148.68   $148.70   $148.70  
  Purchase #6 $223.46   10.223%   $246.3043   $246.30   $246.30   $246.30  
  Purchase #7 $34.66   12.400%   $38.9578   $38.96   $38.95   $39.00  
  7 purchase totals = $877.91       $952.9270   $952.93   $952.95   $953.00