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 $106.25   6.204%   $112.8418   $112.84   $112.85   $112.80  
  Purchase #2 $69.82   4.745%   $73.133   $73.13   $73.15   $73.10  
  Purchase #3 $24.36   4.303%   $25.4082   $25.41   $25.40   $25.40  
  Purchase #4 $223.68   6.648%   $238.5502   $238.55   $238.55   $238.60  
  Purchase #5 $114.91   10.713%   $127.2203   $127.22   $127.20   $127.20  
  Purchase #6 $181.68   13.382%   $205.9924   $205.99   $206.00   $206.00  
  Purchase #7 $83.51   7.602%   $89.8584   $89.86   $89.85   $89.90  
  7 purchase totals = $804.21       $873.0043   $873.00   $873.00   $873.00