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	$37.44	9.380%	$40.9519	$40.95	$40.95	$41.00
Purchase #2	$31.44	3.341%	$32.4904	$32.49	$32.50	$32.50
Purchase #3	$189.59	5.287%	$199.6136	$199.61	$199.60	$199.60
Purchase #4	$164.71	9.119%	$179.7299	$179.73	$179.75	$179.70
Purchase #5	$99.69	10.841%	$110.4974	$110.50	$110.50	$110.50
Purchase #6	$60.78	8.768%	$66.1092	$66.11	$66.10	$66.10
Purchase #7	$99.39	7.140%	$106.4864	$106.49	$106.50	$106.50
7 purchase totals =	$683.04		$735.8788	$735.88	$735.90	$735.90