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	$27.89	7.198%	$29.8975	$29.90	$29.90	$29.90
Purchase #2	$39.90	8.674%	$43.3609	$43.36	$43.35	$43.40
Purchase #3	$20.48	12.290%	$22.997	$23.00	$23.00	$23.00
Purchase #4	$62.32	7.427%	$66.9485	$66.95	$66.95	$66.90
Purchase #5	$100.77	5.820%	$106.6348	$106.63	$106.65	$106.60
Purchase #6	$136.28	9.154%	$148.7551	$148.76	$148.75	$148.80
Purchase #7	$70.71	11.111%	$78.5666	$78.57	$78.55	$78.60
7 purchase totals =	$458.35		$497.1604	$497.17	$497.15	$497.20