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 $60.76   4.376%   $63.4189   $63.42   $63.40   $63.40  
  Purchase #2 $141.27   4.315%   $147.3658   $147.37   $147.35   $147.40  
  Purchase #3 $203.93   12.631%   $229.6884   $229.69   $229.70   $229.70  
  Purchase #4 $154.77   5.774%   $163.7064   $163.71   $163.70   $163.70  
  Purchase #5 $194.37   3.539%   $201.2488   $201.25   $201.25   $201.20  
  Purchase #6 $36.63   11.657%   $40.9   $40.90   $40.90   $40.90  
  Purchase #7 $120.72   13.501%   $137.0184   $137.02   $137.00   $137.00  
  7 purchase totals = $912.45       $983.3467   $983.36   $983.30   $983.30