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	$137.29	10.529%	$151.7453	$151.75	$151.75	$151.70
Purchase #2	$50.67	3.199%	$52.2909	$52.29	$52.30	$52.30
Purchase #3	$162.70	7.113%	$174.2729	$174.27	$174.25	$174.30
Purchase #4	$70.25	3.750%	$72.8844	$72.88	$72.90	$72.90
Purchase #5	$146.82	3.188%	$151.5006	$151.50	$151.50	$151.50
Purchase #6	$8.90	8.524%	$9.6586	$9.66	$9.65	$9.70
Purchase #7	$42.68	13.445%	$48.4183	$48.42	$48.40	$48.40
7 purchase totals =	$619.31		$660.7710	$660.77	$660.75	$660.80