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	$142.70	5.653%	$150.7668	$150.77	$150.75	$150.80
Purchase #2	$165.27	12.248%	$185.5123	$185.51	$185.50	$185.50
Purchase #3	$140.26	13.292%	$158.9034	$158.90	$158.90	$158.90
Purchase #4	$78.34	6.580%	$83.4948	$83.49	$83.50	$83.50
Purchase #5	$66.27	5.236%	$69.7399	$69.74	$69.75	$69.70
Purchase #6	$204.74	13.427%	$232.2304	$232.23	$232.25	$232.20
Purchase #7	$33.51	12.172%	$37.5888	$37.59	$37.60	$37.60
7 purchase totals =	$831.09		$918.2364	$918.23	$918.25	$918.20