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	$137.69	13.700%	$156.5535	$156.55	$156.55	$156.60
Purchase #2	$82.94	6.244%	$88.1188	$88.12	$88.10	$88.10
Purchase #3	$82.59	9.735%	$90.6301	$90.63	$90.65	$90.60
Purchase #4	$157.70	4.220%	$164.3549	$164.35	$164.35	$164.40
Purchase #5	$50.98	11.205%	$56.6923	$56.69	$56.70	$56.70
Purchase #6	$148.74	4.871%	$155.9851	$155.99	$156.00	$156.00
Purchase #7	$247.28	3.835%	$256.7632	$256.76	$256.75	$256.80
7 purchase totals =	$907.92		$969.0979	$969.09	$969.10	$969.20