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	$83.82	6.588%	$89.3421	$89.34	$89.35	$89.30
Purchase #2	$160.81	4.130%	$167.4515	$167.45	$167.45	$167.50
Purchase #3	$180.65	11.135%	$200.7654	$200.77	$200.75	$200.80
Purchase #4	$206.46	4.512%	$215.7755	$215.78	$215.80	$215.80
Purchase #5	$176.58	13.196%	$199.8815	$199.88	$199.90	$199.90
Purchase #6	$105.75	8.168%	$114.3877	$114.39	$114.40	$114.40
Purchase #7	$48.32	9.573%	$52.9457	$52.95	$52.95	$52.90
7 purchase totals =	$962.39		$1,040.5494	$1,040.56	$1,040.60	$1,040.60