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	$247.96	10.801%	$274.7422	$274.74	$274.75	$274.70
Purchase #2	$57.43	5.297%	$60.4721	$60.47	$60.45	$60.50
Purchase #3	$230.40	12.119%	$258.3222	$258.32	$258.30	$258.30
Purchase #4	$158.33	3.591%	$164.0156	$164.02	$164.00	$164.00
Purchase #5	$18.39	11.737%	$20.5484	$20.55	$20.55	$20.50
Purchase #6	$171.45	11.816%	$191.7085	$191.71	$191.70	$191.70
Purchase #7	$106.71	4.775%	$111.8054	$111.81	$111.80	$111.80
7 purchase totals =	$990.67		$1,081.6144	$1,081.62	$1,081.55	$1,081.50