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	$41.36	3.388%	$42.7613	$42.76	$42.75	$42.80
Purchase #2	$162.85	3.319%	$168.255	$168.26	$168.25	$168.30
Purchase #3	$235.86	13.322%	$267.2813	$267.28	$267.30	$267.30
Purchase #4	$90.47	11.831%	$101.1735	$101.17	$101.15	$101.20
Purchase #5	$78.45	5.456%	$82.7302	$82.73	$82.75	$82.70
Purchase #6	$39.87	6.796%	$42.5796	$42.58	$42.60	$42.60
Purchase #7	$101.74	7.159%	$109.0236	$109.02	$109.00	$109.00
7 purchase totals =	$750.60		$813.8045	$813.80	$813.80	$813.90