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	$203.33	12.240%	$228.2176	$228.22	$228.20	$228.20
Purchase #2	$44.82	8.563%	$48.6579	$48.66	$48.65	$48.70
Purchase #3	$134.42	11.642%	$150.0692	$150.07	$150.05	$150.10
Purchase #4	$17.26	4.731%	$18.0766	$18.08	$18.10	$18.10
Purchase #5	$83.70	13.833%	$95.2782	$95.28	$95.30	$95.30
Purchase #6	$99.42	10.550%	$109.9088	$109.91	$109.90	$109.90
Purchase #7	$99.83	12.438%	$112.2469	$112.25	$112.25	$112.20
7 purchase totals =	$682.78		$762.4552	$762.47	$762.45	$762.50