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 $244.45   8.728%   $265.7856   $265.79   $265.80   $265.80  
  Purchase #2 $118.54   3.237%   $122.3771   $122.38   $122.40   $122.40  
  Purchase #3 $61.64   9.497%   $67.494   $67.49   $67.50   $67.50  
  Purchase #4 $61.57   4.869%   $64.5678   $64.57   $64.55   $64.60  
  Purchase #5 $117.83   4.615%   $123.2679   $123.27   $123.25   $123.30  
  Purchase #6 $180.98   13.283%   $205.0196   $205.02   $205.00   $205.00  
  Purchase #7 $118.99   5.170%   $125.1418   $125.14   $125.15   $125.10  
  7 purchase totals = $904.00       $973.6538   $973.66   $973.65   $973.70