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	$89.59	11.435%	$99.8346	$99.83	$99.85	$99.80
Purchase #2	$185.67	13.705%	$211.1161	$211.12	$211.10	$211.10
Purchase #3	$164.45	10.375%	$181.5117	$181.51	$181.50	$181.50
Purchase #4	$44.73	8.246%	$48.4184	$48.42	$48.40	$48.40
Purchase #5	$34.85	12.539%	$39.2198	$39.22	$39.20	$39.20
Purchase #6	$232.89	6.346%	$247.6692	$247.67	$247.65	$247.70
Purchase #7	$124.88	10.455%	$137.9362	$137.94	$137.95	$137.90
7 purchase totals =	$877.06		$965.7060	$965.71	$965.65	$965.60