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	$40.38	6.223%	$42.8928	$42.89	$42.90	$42.90
Purchase #2	$148.89	12.109%	$166.9191	$166.92	$166.90	$166.90
Purchase #3	$164.89	3.412%	$170.516	$170.52	$170.50	$170.50
Purchase #4	$249.54	9.514%	$273.2812	$273.28	$273.30	$273.30
Purchase #5	$123.51	5.609%	$130.4377	$130.44	$130.45	$130.40
Purchase #6	$157.86	9.645%	$173.0856	$173.09	$173.10	$173.10
Purchase #7	$168.84	10.342%	$186.3014	$186.30	$186.30	$186.30
7 purchase totals =	$1,053.91		$1,143.4338	$1,143.44	$1,143.45	$1,143.40