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	$100.33	6.290%	$106.6408	$106.64	$106.65	$106.60
Purchase #2	$223.88	8.698%	$243.3531	$243.35	$243.35	$243.40
Purchase #3	$29.42	9.102%	$32.0978	$32.10	$32.10	$32.10
Purchase #4	$57.39	3.260%	$59.2609	$59.26	$59.25	$59.30
Purchase #5	$119.61	7.191%	$128.2112	$128.21	$128.20	$128.20
Purchase #6	$40.33	9.818%	$44.2896	$44.29	$44.30	$44.30
Purchase #7	$93.32	6.756%	$99.6247	$99.62	$99.60	$99.60
7 purchase totals =	$664.28		$713.4781	$713.47	$713.45	$713.50