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 $68.50   11.722%   $76.5296   $76.53   $76.55   $76.50  
  Purchase #2 $118.93   12.619%   $133.9378   $133.94   $133.95   $133.90  
  Purchase #3 $18.42   8.315%   $19.9516   $19.95   $19.95   $20.00  
  Purchase #4 $5.85   10.606%   $6.4705   $6.47   $6.45   $6.50  
  Purchase #5 $195.47   12.291%   $219.4952   $219.50   $219.50   $219.50  
  Purchase #6 $38.92   7.596%   $41.8764   $41.88   $41.90   $41.90  
  Purchase #7 $235.54   4.174%   $245.3714   $245.37   $245.35   $245.40  
  7 purchase totals = $681.63       $743.6325   $743.64   $743.65   $743.70