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 $144.51   3.720%   $149.8858   $149.89   $149.90   $149.90  
  Purchase #2 $215.61   5.395%   $227.2422   $227.24   $227.25   $227.20  
  Purchase #3 $24.72   4.294%   $25.7815   $25.78   $25.80   $25.80  
  Purchase #4 $9.67   11.827%   $10.8137   $10.81   $10.80   $10.80  
  Purchase #5 $116.64   11.249%   $129.7608   $129.76   $129.75   $129.80  
  Purchase #6 $122.36   6.142%   $129.8754   $129.88   $129.90   $129.90  
  Purchase #7 $205.64   5.473%   $216.8947   $216.89   $216.90   $216.90  
  7 purchase totals = $839.15       $890.2541   $890.25   $890.30   $890.30