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	$205.71	6.646%	$219.3815	$219.38	$219.40	$219.40
Purchase #2	$151.55	11.233%	$168.5736	$168.57	$168.55	$168.60
Purchase #3	$102.42	11.606%	$114.3069	$114.31	$114.30	$114.30
Purchase #4	$48.35	12.610%	$54.4469	$54.45	$54.45	$54.40
Purchase #5	$144.42	5.313%	$152.093	$152.09	$152.10	$152.10
Purchase #6	$35.36	6.692%	$37.7263	$37.73	$37.75	$37.70
Purchase #7	$119.87	3.740%	$124.3531	$124.35	$124.35	$124.40
7 purchase totals =	$807.68		$870.8813	$870.88	$870.90	$870.90