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	$132.32	5.123%	$139.0988	$139.10	$139.10	$139.10
Purchase #2	$139.61	11.413%	$155.5437	$155.54	$155.55	$155.50
Purchase #3	$13.47	4.478%	$14.0732	$14.07	$14.05	$14.10
Purchase #4	$19.31	13.446%	$21.9064	$21.91	$21.90	$21.90
Purchase #5	$99.63	6.832%	$106.4367	$106.44	$106.45	$106.40
Purchase #6	$247.77	6.746%	$264.4846	$264.48	$264.50	$264.50
Purchase #7	$144.52	7.584%	$155.4804	$155.48	$155.50	$155.50
7 purchase totals =	$796.63		$857.0238	$857.02	$857.05	$857.00