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	$75.46	5.128%	$79.3296	$79.33	$79.35	$79.30
Purchase #2	$39.72	7.136%	$42.5544	$42.55	$42.55	$42.60
Purchase #3	$212.90	10.761%	$235.8102	$235.81	$235.80	$235.80
Purchase #4	$206.28	6.351%	$219.3808	$219.38	$219.40	$219.40
Purchase #5	$132.41	13.604%	$150.4231	$150.42	$150.40	$150.40
Purchase #6	$238.50	12.129%	$267.4277	$267.43	$267.45	$267.40
Purchase #7	$21.39	13.240%	$24.222	$24.22	$24.20	$24.20
7 purchase totals =	$926.66		$1,019.1478	$1,019.14	$1,019.15	$1,019.10