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	$185.40	12.710%	$208.9643	$208.96	$208.95	$209.00
Purchase #2	$37.72	6.873%	$40.3125	$40.31	$40.30	$40.30
Purchase #3	$174.33	10.512%	$192.6556	$192.66	$192.65	$192.70
Purchase #4	$98.87	11.801%	$110.5376	$110.54	$110.55	$110.50
Purchase #5	$41.41	10.331%	$45.6881	$45.69	$45.70	$45.70
Purchase #6	$155.83	12.482%	$175.2807	$175.28	$175.30	$175.30
Purchase #7	$165.50	12.392%	$186.0088	$186.01	$186.00	$186.00
7 purchase totals =	$859.06		$959.4476	$959.45	$959.45	$959.50