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 $59.54   5.557%   $62.8486   $62.85   $62.85   $62.80  
  Purchase #2 $41.95   8.811%   $45.6462   $45.65   $45.65   $45.60  
  Purchase #3 $86.96   6.602%   $92.7011   $92.70   $92.70   $92.70  
  Purchase #4 $108.41   11.506%   $120.8837   $120.88   $120.90   $120.90  
  Purchase #5 $175.38   4.841%   $183.8701   $183.87   $183.85   $183.90  
  Purchase #6 $214.30   13.350%   $242.9091   $242.91   $242.90   $242.90  
  Purchase #7 $83.78   10.288%   $92.3993   $92.40   $92.40   $92.40  
  7 purchase totals = $770.32       $841.2581   $841.26   $841.25   $841.20