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	$246.58	4.289%	$257.1558	$257.16	$257.15	$257.20
Purchase #2	$135.67	12.272%	$152.3194	$152.32	$152.30	$152.30
Purchase #3	$57.54	4.678%	$60.2317	$60.23	$60.25	$60.20
Purchase #4	$124.79	5.435%	$131.5723	$131.57	$131.55	$131.60
Purchase #5	$160.83	11.124%	$178.7207	$178.72	$178.70	$178.70
Purchase #6	$118.39	4.267%	$123.4417	$123.44	$123.45	$123.40
Purchase #7	$67.67	13.610%	$76.8799	$76.88	$76.90	$76.90
7 purchase totals =	$911.47		$980.3215	$980.32	$980.30	$980.30