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	$85.87	5.272%	$90.3971	$90.40	$90.40	$90.40
Purchase #2	$238.48	13.746%	$271.2615	$271.26	$271.25	$271.30
Purchase #3	$158.58	3.612%	$164.3079	$164.31	$164.30	$164.30
Purchase #4	$140.76	11.286%	$156.6462	$156.65	$156.65	$156.60
Purchase #5	$140.39	5.309%	$147.8433	$147.84	$147.85	$147.80
Purchase #6	$17.29	10.750%	$19.1487	$19.15	$19.15	$19.10
Purchase #7	$52.39	11.751%	$58.5463	$58.55	$58.55	$58.50
7 purchase totals =	$833.76		$908.1510	$908.16	$908.15	$908.00