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	$243.72	13.835%	$277.4387	$277.44	$277.45	$277.40
Purchase #2	$90.47	11.332%	$100.7221	$100.72	$100.70	$100.70
Purchase #3	$179.42	9.464%	$196.4003	$196.40	$196.40	$196.40
Purchase #4	$53.30	11.742%	$59.5585	$59.56	$59.55	$59.60
Purchase #5	$26.34	7.602%	$28.3424	$28.34	$28.35	$28.30
Purchase #6	$206.86	12.528%	$232.7754	$232.78	$232.80	$232.80
Purchase #7	$207.61	8.870%	$226.025	$226.03	$226.05	$226.00
7 purchase totals =	$1,007.72		$1,121.2624	$1,121.27	$1,121.30	$1,121.20