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	$171.33	8.456%	$185.8177	$185.82	$185.80	$185.80
Purchase #2	$150.31	6.598%	$160.2275	$160.23	$160.25	$160.20
Purchase #3	$164.85	12.260%	$185.0606	$185.06	$185.05	$185.10
Purchase #4	$113.46	10.829%	$125.7466	$125.75	$125.75	$125.70
Purchase #5	$149.69	12.581%	$168.5225	$168.52	$168.50	$168.50
Purchase #6	$250.27	13.134%	$283.1405	$283.14	$283.15	$283.10
Purchase #7	$106.27	11.105%	$118.0713	$118.07	$118.05	$118.10
7 purchase totals =	$1,106.18		$1,226.5867	$1,226.59	$1,226.55	$1,226.50