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	$142.53	6.526%	$151.8315	$151.83	$151.85	$151.80
Purchase #2	$64.86	3.634%	$67.217	$67.22	$67.20	$67.20
Purchase #3	$199.71	4.657%	$209.0105	$209.01	$209.00	$209.00
Purchase #4	$65.95	8.654%	$71.6573	$71.66	$71.65	$71.70
Purchase #5	$81.61	9.852%	$89.6502	$89.65	$89.65	$89.70
Purchase #6	$239.72	4.741%	$251.0851	$251.09	$251.10	$251.10
Purchase #7	$141.32	8.321%	$153.0792	$153.08	$153.10	$153.10
7 purchase totals =	$935.70		$993.5308	$993.54	$993.55	$993.60