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	$166.72	13.239%	$188.7921	$188.79	$188.80	$188.80
Purchase #2	$173.34	13.207%	$196.233	$196.23	$196.25	$196.20
Purchase #3	$184.73	6.540%	$196.8113	$196.81	$196.80	$196.80
Purchase #4	$161.72	10.844%	$179.2569	$179.26	$179.25	$179.30
Purchase #5	$126.63	8.568%	$137.4797	$137.48	$137.50	$137.50
Purchase #6	$240.81	10.850%	$266.9379	$266.94	$266.95	$266.90
Purchase #7	$29.61	3.813%	$30.739	$30.74	$30.75	$30.70
7 purchase totals =	$1,083.56		$1,196.2499	$1,196.25	$1,196.30	$1,196.20