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	$93.28	6.315%	$99.1706	$99.17	$99.15	$99.20
Purchase #2	$222.96	3.420%	$230.5852	$230.59	$230.60	$230.60
Purchase #3	$244.26	12.874%	$275.706	$275.71	$275.70	$275.70
Purchase #4	$198.94	11.861%	$222.5363	$222.54	$222.55	$222.50
Purchase #5	$141.62	11.586%	$158.0281	$158.03	$158.05	$158.00
Purchase #6	$97.47	6.124%	$103.4391	$103.44	$103.45	$103.40
Purchase #7	$146.83	3.407%	$151.8325	$151.83	$151.85	$151.80
7 purchase totals =	$1,145.36		$1,241.2978	$1,241.31	$1,241.35	$1,241.20