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	$70.65	9.259%	$77.1915	$77.19	$77.20	$77.20
Purchase #2	$91.51	9.840%	$100.5146	$100.51	$100.50	$100.50
Purchase #3	$214.72	12.197%	$240.9094	$240.91	$240.90	$240.90
Purchase #4	$111.93	5.687%	$118.2955	$118.30	$118.30	$118.30
Purchase #5	$219.88	12.867%	$248.172	$248.17	$248.15	$248.20
Purchase #6	$75.48	3.207%	$77.9006	$77.90	$77.90	$77.90
Purchase #7	$112.49	5.712%	$118.9154	$118.92	$118.90	$118.90
7 purchase totals =	$896.66		$981.8990	$981.90	$981.85	$981.90