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	$40.80	4.116%	$42.4793	$42.48	$42.50	$42.50
Purchase #2	$19.48	11.330%	$21.6871	$21.69	$21.70	$21.70
Purchase #3	$190.66	11.608%	$212.7918	$212.79	$212.80	$212.80
Purchase #4	$248.96	6.136%	$264.2362	$264.24	$264.25	$264.20
Purchase #5	$82.50	10.497%	$91.16	$91.16	$91.15	$91.20
Purchase #6	$10.77	9.869%	$11.8329	$11.83	$11.85	$11.80
Purchase #7	$192.27	12.569%	$216.4364	$216.44	$216.45	$216.40
7 purchase totals =	$785.44		$860.6237	$860.63	$860.70	$860.60