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 $190.37   8.609%   $206.759   $206.76   $206.75   $206.80  
  Purchase #2 $20.38   6.240%   $21.6517   $21.65   $21.65   $21.70  
  Purchase #3 $120.45   10.564%   $133.1743   $133.17   $133.15   $133.20  
  Purchase #4 $106.79   11.848%   $119.4425   $119.44   $119.45   $119.40  
  Purchase #5 $85.28   10.858%   $94.5397   $94.54   $94.55   $94.50  
  Purchase #6 $195.27   8.752%   $212.36   $212.36   $212.35   $212.40  
  Purchase #7 $147.64   11.353%   $164.4016   $164.40   $164.40   $164.40  
  7 purchase totals = $866.18       $952.3288   $952.32   $952.30   $952.40