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	$124.83	11.600%	$139.3103	$139.31	$139.30	$139.30
Purchase #2	$121.26	10.276%	$133.7207	$133.72	$133.70	$133.70
Purchase #3	$95.74	4.224%	$99.7841	$99.78	$99.80	$99.80
Purchase #4	$77.97	9.395%	$85.2953	$85.30	$85.30	$85.30
Purchase #5	$209.83	3.126%	$216.3893	$216.39	$216.40	$216.40
Purchase #6	$157.70	5.689%	$166.6716	$166.67	$166.65	$166.70
Purchase #7	$230.31	4.385%	$240.4091	$240.41	$240.40	$240.40
7 purchase totals =	$1,017.64		$1,081.5804	$1,081.58	$1,081.55	$1,081.60