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	$109.96	13.301%	$124.5858	$124.59	$124.60	$124.60
Purchase #2	$91.55	6.118%	$97.151	$97.15	$97.15	$97.20
Purchase #3	$204.40	3.780%	$212.1263	$212.13	$212.15	$212.10
Purchase #4	$10.73	7.490%	$11.5337	$11.53	$11.55	$11.50
Purchase #5	$43.71	7.266%	$46.886	$46.89	$46.90	$46.90
Purchase #6	$75.45	4.150%	$78.5812	$78.58	$78.60	$78.60
Purchase #7	$224.88	6.177%	$238.7708	$238.77	$238.75	$238.80
7 purchase totals =	$760.68		$809.6348	$809.64	$809.70	$809.70