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 $84.79   13.602%   $96.3231   $96.32   $96.30   $96.30  
  Purchase #2 $158.26   7.608%   $170.3004   $170.30   $170.30   $170.30  
  Purchase #3 $118.48   9.448%   $129.674   $129.67   $129.65   $129.70  
  Purchase #4 $122.86   7.414%   $131.9688   $131.97   $131.95   $132.00  
  Purchase #5 $155.33   10.228%   $171.2172   $171.22   $171.20   $171.20  
  Purchase #6 $175.99   8.248%   $190.5057   $190.51   $190.50   $190.50  
  Purchase #7 $144.83   12.561%   $163.0221   $163.02   $163.00   $163.00  
  7 purchase totals = $960.54       $1,053.0113   $1,053.01   $1,052.90   $1,053.00