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 $103.64   9.766%   $113.7615   $113.76   $113.75   $113.80  
  Purchase #2 $248.26   13.306%   $281.2935   $281.29   $281.30   $281.30  
  Purchase #3 $47.94   3.106%   $49.429   $49.43   $49.45   $49.40  
  Purchase #4 $236.91   12.350%   $266.1684   $266.17   $266.15   $266.20  
  Purchase #5 $83.99   8.270%   $90.936   $90.94   $90.95   $90.90  
  Purchase #6 $50.27   11.322%   $55.9616   $55.96   $55.95   $56.00  
  Purchase #7 $42.79   6.207%   $45.446   $45.45   $45.45   $45.40  
  7 purchase totals = $813.80       $902.9960   $903.00   $903.00   $903.00