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	$101.86	7.226%	$109.2204	$109.22	$109.20	$109.20
Purchase #2	$194.68	8.135%	$210.5172	$210.52	$210.50	$210.50
Purchase #3	$160.32	12.259%	$179.9736	$179.97	$179.95	$180.00
Purchase #4	$9.55	11.234%	$10.6228	$10.62	$10.60	$10.60
Purchase #5	$89.77	12.396%	$100.8979	$100.90	$100.90	$100.90
Purchase #6	$80.59	12.216%	$90.4349	$90.43	$90.45	$90.40
Purchase #7	$223.75	10.223%	$246.624	$246.62	$246.60	$246.60
7 purchase totals =	$860.52		$948.2908	$948.28	$948.20	$948.20