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	$112.59	10.594%	$124.5178	$124.52	$124.50	$124.50
Purchase #2	$25.50	3.163%	$26.3066	$26.31	$26.30	$26.30
Purchase #3	$177.72	8.528%	$192.876	$192.88	$192.90	$192.90
Purchase #4	$85.65	4.233%	$89.2756	$89.28	$89.30	$89.30
Purchase #5	$177.50	7.651%	$191.0805	$191.08	$191.10	$191.10
Purchase #6	$85.93	10.493%	$94.9466	$94.95	$94.95	$94.90
Purchase #7	$195.88	10.515%	$216.4768	$216.48	$216.50	$216.50
7 purchase totals =	$860.77		$935.4799	$935.50	$935.55	$935.50