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	$165.77	8.719%	$180.2235	$180.22	$180.20	$180.20
Purchase #2	$236.99	13.535%	$269.0666	$269.07	$269.05	$269.10
Purchase #3	$78.29	9.219%	$85.5076	$85.51	$85.50	$85.50
Purchase #4	$31.73	12.863%	$35.8114	$35.81	$35.80	$35.80
Purchase #5	$6.83	10.327%	$7.5353	$7.54	$7.55	$7.50
Purchase #6	$101.41	12.118%	$113.6989	$113.70	$113.70	$113.70
Purchase #7	$239.91	4.476%	$250.6484	$250.65	$250.65	$250.60
7 purchase totals =	$860.93		$942.4917	$942.50	$942.45	$942.40