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	$240.74	6.358%	$256.0462	$256.05	$256.05	$256.00
Purchase #2	$143.89	6.489%	$153.227	$153.23	$153.25	$153.20
Purchase #3	$34.43	10.608%	$38.0823	$38.08	$38.10	$38.10
Purchase #4	$131.27	12.170%	$147.2456	$147.25	$147.25	$147.20
Purchase #5	$134.65	5.632%	$142.2335	$142.23	$142.25	$142.20
Purchase #6	$82.32	11.241%	$91.5736	$91.57	$91.55	$91.60
Purchase #7	$218.33	11.139%	$242.6498	$242.65	$242.65	$242.60
7 purchase totals =	$985.63		$1,071.0580	$1,071.06	$1,071.10	$1,070.90