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	$29.65	9.655%	$32.5127	$32.51	$32.50	$32.50
Purchase #2	$159.60	4.834%	$167.3151	$167.32	$167.30	$167.30
Purchase #3	$62.47	13.707%	$71.0328	$71.03	$71.05	$71.00
Purchase #4	$236.94	9.220%	$258.7859	$258.79	$258.80	$258.80
Purchase #5	$7.74	9.247%	$8.4557	$8.46	$8.45	$8.50
Purchase #6	$196.65	4.168%	$204.8464	$204.85	$204.85	$204.80
Purchase #7	$39.46	6.774%	$42.133	$42.13	$42.15	$42.10
7 purchase totals =	$732.51		$785.0816	$785.09	$785.10	$785.00