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 $54.69   5.308%   $57.5929   $57.59   $57.60   $57.60  
  Purchase #2 $234.28   8.141%   $253.3527   $253.35   $253.35   $253.40  
  Purchase #3 $68.82   4.843%   $72.153   $72.15   $72.15   $72.20  
  Purchase #4 $166.58   10.437%   $183.966   $183.97   $183.95   $184.00  
  Purchase #5 $186.41   9.343%   $203.8263   $203.83   $203.85   $203.80  
  Purchase #6 $67.55   12.652%   $76.0964   $76.10   $76.10   $76.10  
  Purchase #7 $118.78   12.103%   $133.1559   $133.16   $133.15   $133.20  
  7 purchase totals = $897.11       $980.1432   $980.15   $980.15   $980.30