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	$126.73	13.706%	$144.0996	$144.10	$144.10	$144.10
Purchase #2	$15.85	13.585%	$18.0032	$18.00	$18.00	$18.00
Purchase #3	$146.72	6.799%	$156.6955	$156.70	$156.70	$156.70
Purchase #4	$132.64	8.648%	$144.1107	$144.11	$144.10	$144.10
Purchase #5	$147.37	10.427%	$162.7363	$162.74	$162.75	$162.70
Purchase #6	$137.50	6.486%	$146.4183	$146.42	$146.40	$146.40
Purchase #7	$46.33	13.812%	$52.7291	$52.73	$52.75	$52.70
7 purchase totals =	$753.14		$824.7927	$824.80	$824.80	$824.70