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	$221.42	12.220%	$248.4775	$248.48	$248.50	$248.50
Purchase #2	$72.81	13.698%	$82.7835	$82.78	$82.80	$82.80
Purchase #3	$238.28	6.230%	$253.1248	$253.12	$253.10	$253.10
Purchase #4	$110.96	11.158%	$123.3409	$123.34	$123.35	$123.30
Purchase #5	$77.47	12.580%	$87.2157	$87.22	$87.20	$87.20
Purchase #6	$83.60	4.784%	$87.5994	$87.60	$87.60	$87.60
Purchase #7	$199.83	5.522%	$210.8646	$210.86	$210.85	$210.90
7 purchase totals =	$1,004.37		$1,093.4064	$1,093.40	$1,093.40	$1,093.40