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	$89.37	11.203%	$99.3821	$99.38	$99.40	$99.40
Purchase #2	$145.64	4.494%	$152.1851	$152.19	$152.20	$152.20
Purchase #3	$123.40	9.142%	$134.6812	$134.68	$134.70	$134.70
Purchase #4	$132.51	9.789%	$145.4814	$145.48	$145.50	$145.50
Purchase #5	$174.80	9.180%	$190.8466	$190.85	$190.85	$190.80
Purchase #6	$82.57	9.516%	$90.4274	$90.43	$90.45	$90.40
Purchase #7	$138.32	7.174%	$148.2431	$148.24	$148.25	$148.20
7 purchase totals =	$886.61		$961.2469	$961.25	$961.35	$961.20