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	$79.84	11.753%	$89.2236	$89.22	$89.20	$89.20
Purchase #2	$100.85	10.828%	$111.77	$111.77	$111.75	$111.80
Purchase #3	$11.32	3.705%	$11.7394	$11.74	$11.75	$11.70
Purchase #4	$247.53	11.673%	$276.4242	$276.42	$276.40	$276.40
Purchase #5	$164.73	11.718%	$184.0331	$184.03	$184.05	$184.00
Purchase #6	$107.48	4.146%	$111.9361	$111.94	$111.95	$111.90
Purchase #7	$82.98	10.824%	$91.9618	$91.96	$91.95	$92.00
7 purchase totals =	$794.73		$877.0882	$877.08	$877.05	$877.00