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	$136.39	11.139%	$151.5825	$151.58	$151.60	$151.60
Purchase #2	$22.48	8.673%	$24.4297	$24.43	$24.45	$24.40
Purchase #3	$169.31	6.216%	$179.8343	$179.83	$179.85	$179.80
Purchase #4	$56.37	3.134%	$58.1366	$58.14	$58.15	$58.10
Purchase #5	$82.51	3.422%	$85.3335	$85.33	$85.35	$85.30
Purchase #6	$223.35	12.155%	$250.4982	$250.50	$250.50	$250.50
Purchase #7	$61.51	3.560%	$63.6998	$63.70	$63.70	$63.70
7 purchase totals =	$751.92		$813.5146	$813.51	$813.60	$813.40