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	$166.58	12.853%	$187.9905	$187.99	$188.00	$188.00
Purchase #2	$238.91	8.502%	$259.2221	$259.22	$259.20	$259.20
Purchase #3	$153.57	12.613%	$172.9398	$172.94	$172.95	$172.90
Purchase #4	$205.33	4.751%	$215.0852	$215.09	$215.10	$215.10
Purchase #5	$38.41	10.779%	$42.5502	$42.55	$42.55	$42.60
Purchase #6	$103.50	7.700%	$111.4695	$111.47	$111.45	$111.50
Purchase #7	$204.57	7.570%	$220.0559	$220.06	$220.05	$220.10
7 purchase totals =	$1,110.87		$1,209.3132	$1,209.32	$1,209.30	$1,209.40