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	$103.31	6.497%	$110.0221	$110.02	$110.00	$110.00
Purchase #2	$116.81	11.201%	$129.8939	$129.89	$129.90	$129.90
Purchase #3	$51.89	13.493%	$58.8915	$58.89	$58.90	$58.90
Purchase #4	$50.69	6.267%	$53.8667	$53.87	$53.85	$53.90
Purchase #5	$56.84	5.350%	$59.8809	$59.88	$59.90	$59.90
Purchase #6	$190.40	4.830%	$199.5963	$199.60	$199.60	$199.60
Purchase #7	$245.33	12.376%	$275.692	$275.69	$275.70	$275.70
7 purchase totals =	$815.27		$887.8434	$887.84	$887.85	$887.90