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	$30.40	10.422%	$33.5683	$33.57	$33.55	$33.60
Purchase #2	$179.75	13.706%	$204.3865	$204.39	$204.40	$204.40
Purchase #3	$35.94	13.408%	$40.7588	$40.76	$40.75	$40.80
Purchase #4	$23.58	10.334%	$26.0168	$26.02	$26.00	$26.00
Purchase #5	$65.38	10.697%	$72.3737	$72.37	$72.35	$72.40
Purchase #6	$19.92	12.332%	$22.3765	$22.38	$22.40	$22.40
Purchase #7	$174.34	6.635%	$185.9075	$185.91	$185.90	$185.90
7 purchase totals =	$529.31		$585.3881	$585.40	$585.35	$585.50