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 $111.34   4.185%   $115.9996   $116.00   $116.00   $116.00  
  Purchase #2 $127.93   4.306%   $133.4387   $133.44   $133.45   $133.40  
  Purchase #3 $234.54   4.261%   $244.5337   $244.53   $244.55   $244.50  
  Purchase #4 $243.27   12.454%   $273.5668   $273.57   $273.55   $273.60  
  Purchase #5 $221.78   11.196%   $246.6105   $246.61   $246.60   $246.60  
  Purchase #6 $113.29   9.657%   $124.2304   $124.23   $124.25   $124.20  
  Purchase #7 $241.81   8.456%   $262.2575   $262.26   $262.25   $262.30  
  7 purchase totals = $1,293.96       $1,400.6372   $1,400.64   $1,400.65   $1,400.60