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	$28.32	12.847%	$31.9583	$31.96	$31.95	$32.00
Purchase #2	$221.54	13.531%	$251.5166	$251.52	$251.50	$251.50
Purchase #3	$53.31	11.526%	$59.4545	$59.45	$59.45	$59.50
Purchase #4	$209.54	4.762%	$219.5183	$219.52	$219.50	$219.50
Purchase #5	$37.48	13.406%	$42.5046	$42.50	$42.50	$42.50
Purchase #6	$228.69	3.453%	$236.5867	$236.59	$236.60	$236.60
Purchase #7	$152.31	12.162%	$170.8339	$170.83	$170.85	$170.80
7 purchase totals =	$931.19		$1,012.3729	$1,012.37	$1,012.35	$1,012.40