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	$169.72	12.858%	$191.5426	$191.54	$191.55	$191.50
Purchase #2	$65.32	8.302%	$70.7429	$70.74	$70.75	$70.70
Purchase #3	$151.44	4.457%	$158.1897	$158.19	$158.20	$158.20
Purchase #4	$147.51	13.458%	$167.3619	$167.36	$167.35	$167.40
Purchase #5	$53.75	6.676%	$57.3384	$57.34	$57.35	$57.30
Purchase #6	$66.38	6.733%	$70.8494	$70.85	$70.85	$70.80
Purchase #7	$50.72	6.140%	$53.8342	$53.83	$53.85	$53.80
7 purchase totals =	$704.84		$769.8591	$769.85	$769.90	$769.70