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	$43.70	11.809%	$48.8605	$48.86	$48.85	$48.90
Purchase #2	$134.51	13.380%	$152.5074	$152.51	$152.50	$152.50
Purchase #3	$169.74	10.467%	$187.5067	$187.51	$187.50	$187.50
Purchase #4	$233.46	10.569%	$258.1344	$258.13	$258.15	$258.10
Purchase #5	$51.75	7.305%	$55.5303	$55.53	$55.55	$55.50
Purchase #6	$29.65	8.860%	$32.277	$32.28	$32.30	$32.30
Purchase #7	$80.30	6.219%	$85.2939	$85.29	$85.30	$85.30
7 purchase totals =	$743.11		$820.1102	$820.11	$820.15	$820.10