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	$120.38	9.464%	$131.7728	$131.77	$131.75	$131.80
Purchase #2	$216.53	10.175%	$238.5619	$238.56	$238.55	$238.60
Purchase #3	$153.43	7.585%	$165.0677	$165.07	$165.05	$165.10
Purchase #4	$48.56	8.665%	$52.7677	$52.77	$52.75	$52.80
Purchase #5	$16.91	3.180%	$17.4477	$17.45	$17.45	$17.40
Purchase #6	$137.46	13.154%	$155.5415	$155.54	$155.55	$155.50
Purchase #7	$42.32	7.299%	$45.4089	$45.41	$45.40	$45.40
7 purchase totals =	$735.59		$806.5682	$806.57	$806.50	$806.60