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 $68.25   11.793%   $76.2987   $76.30   $76.30   $76.30  
  Purchase #2 $142.72   5.523%   $150.6024   $150.60   $150.60   $150.60  
  Purchase #3 $163.54   10.639%   $180.939   $180.94   $180.95   $180.90  
  Purchase #4 $8.88   4.402%   $9.2709   $9.27   $9.25   $9.30  
  Purchase #5 $45.86   12.327%   $51.5132   $51.51   $51.50   $51.50  
  Purchase #6 $195.30   10.845%   $216.4803   $216.48   $216.50   $216.50  
  Purchase #7 $119.26   3.564%   $123.5104   $123.51   $123.50   $123.50  
  7 purchase totals = $743.81       $808.6149   $808.61   $808.60   $808.60