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 $218.41   3.715%   $226.5239   $226.52   $226.50   $226.50  
  Purchase #2 $58.47   3.791%   $60.6866   $60.69   $60.70   $60.70  
  Purchase #3 $7.64   4.452%   $7.9801   $7.98   $8.00   $8.00  
  Purchase #4 $107.51   13.269%   $121.7755   $121.78   $121.80   $121.80  
  Purchase #5 $14.95   6.756%   $15.96   $15.96   $15.95   $16.00  
  Purchase #6 $223.68   13.329%   $253.4943   $253.49   $253.50   $253.50  
  Purchase #7 $95.40   12.416%   $107.2449   $107.24   $107.25   $107.20  
  7 purchase totals = $726.06       $793.6653   $793.66   $793.70   $793.70