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	$171.92	10.723%	$190.355	$190.36	$190.35	$190.40
Purchase #2	$151.84	5.301%	$159.889	$159.89	$159.90	$159.90
Purchase #3	$20.73	12.799%	$23.3832	$23.38	$23.40	$23.40
Purchase #4	$101.77	9.470%	$111.4076	$111.41	$111.40	$111.40
Purchase #5	$219.59	3.674%	$227.6577	$227.66	$227.65	$227.70
Purchase #6	$227.35	10.301%	$250.7693	$250.77	$250.75	$250.80
Purchase #7	$34.34	3.191%	$35.4358	$35.44	$35.45	$35.40
7 purchase totals =	$927.54		$998.8976	$998.91	$998.90	$999.00