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	$89.85	3.686%	$93.1619	$93.16	$93.15	$93.20
Purchase #2	$102.49	7.763%	$110.4463	$110.45	$110.45	$110.40
Purchase #3	$236.73	3.105%	$244.0805	$244.08	$244.10	$244.10
Purchase #4	$64.86	13.299%	$73.4857	$73.49	$73.50	$73.50
Purchase #5	$83.38	7.220%	$89.4	$89.40	$89.40	$89.40
Purchase #6	$157.90	9.108%	$172.2815	$172.28	$172.30	$172.30
Purchase #7	$25.37	8.560%	$27.5417	$27.54	$27.55	$27.50
7 purchase totals =	$760.58		$810.3976	$810.40	$810.45	$810.40