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	$56.32	5.614%	$59.4818	$59.48	$59.50	$59.50
Purchase #2	$89.25	12.753%	$100.6321	$100.63	$100.65	$100.60
Purchase #3	$71.58	8.533%	$77.6879	$77.69	$77.70	$77.70
Purchase #4	$236.39	12.494%	$265.9246	$265.92	$265.90	$265.90
Purchase #5	$60.91	3.118%	$62.8092	$62.81	$62.80	$62.80
Purchase #6	$171.61	7.285%	$184.1118	$184.11	$184.10	$184.10
Purchase #7	$202.66	12.571%	$228.1364	$228.14	$228.15	$228.10
7 purchase totals =	$888.72		$978.7838	$978.78	$978.80	$978.70