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	$128.80	6.414%	$137.0612	$137.06	$137.05	$137.10
Purchase #2	$92.36	10.320%	$101.8916	$101.89	$101.90	$101.90
Purchase #3	$153.74	7.490%	$165.2551	$165.26	$165.25	$165.30
Purchase #4	$38.59	5.621%	$40.7591	$40.76	$40.75	$40.80
Purchase #5	$220.40	9.255%	$240.798	$240.80	$240.80	$240.80
Purchase #6	$92.72	11.634%	$103.507	$103.51	$103.50	$103.50
Purchase #7	$40.30	11.380%	$44.8861	$44.89	$44.90	$44.90
7 purchase totals =	$766.91		$834.1581	$834.17	$834.15	$834.30