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	$70.54	3.345%	$72.8996	$72.90	$72.90	$72.90
Purchase #2	$82.90	9.340%	$90.6429	$90.64	$90.65	$90.60
Purchase #3	$212.95	12.607%	$239.7966	$239.80	$239.80	$239.80
Purchase #4	$140.70	4.337%	$146.8022	$146.80	$146.80	$146.80
Purchase #5	$48.34	5.281%	$50.8928	$50.89	$50.90	$50.90
Purchase #6	$36.72	9.462%	$40.1944	$40.19	$40.20	$40.20
Purchase #7	$174.75	11.335%	$194.5579	$194.56	$194.55	$194.60
7 purchase totals =	$766.90		$835.7864	$835.78	$835.80	$835.80