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 $216.61   12.319%   $243.2942   $243.29   $243.30   $243.30  
  Purchase #2 $106.38   6.842%   $113.6585   $113.66   $113.65   $113.70  
  Purchase #3 $121.48   4.481%   $126.9235   $126.92   $126.90   $126.90  
  Purchase #4 $159.54   10.299%   $175.971   $175.97   $175.95   $176.00  
  Purchase #5 $52.87   3.494%   $54.7173   $54.72   $54.70   $54.70  
  Purchase #6 $119.93   13.820%   $136.5043   $136.50   $136.50   $136.50  
  Purchase #7 $112.69   7.578%   $121.2296   $121.23   $121.25   $121.20  
  7 purchase totals = $889.50       $972.2984   $972.29   $972.25   $972.30