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	$27.33	4.799%	$28.6416	$28.64	$28.65	$28.60
Purchase #2	$53.53	7.827%	$57.7198	$57.72	$57.70	$57.70
Purchase #3	$37.61	8.736%	$40.8956	$40.90	$40.90	$40.90
Purchase #4	$78.47	6.151%	$83.2967	$83.30	$83.30	$83.30
Purchase #5	$15.72	11.559%	$17.5371	$17.54	$17.55	$17.50
Purchase #6	$216.40	10.197%	$238.4663	$238.47	$238.45	$238.50
Purchase #7	$111.69	4.841%	$117.0969	$117.10	$117.10	$117.10
7 purchase totals =	$540.75		$583.6540	$583.67	$583.65	$583.60