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	$39.56	6.276%	$42.0428	$42.04	$42.05	$42.00
Purchase #2	$69.89	12.733%	$78.7891	$78.79	$78.80	$78.80
Purchase #3	$140.39	9.423%	$153.6189	$153.62	$153.60	$153.60
Purchase #4	$177.36	12.809%	$200.078	$200.08	$200.10	$200.10
Purchase #5	$24.59	4.498%	$25.6961	$25.70	$25.70	$25.70
Purchase #6	$16.76	10.674%	$18.549	$18.55	$18.55	$18.50
Purchase #7	$11.58	12.610%	$13.0402	$13.04	$13.05	$13.00
7 purchase totals =	$480.13		$531.8141	$531.82	$531.85	$531.70