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	$49.55	9.554%	$54.284	$54.28	$54.30	$54.30
Purchase #2	$89.65	12.215%	$100.6007	$100.60	$100.60	$100.60
Purchase #3	$172.56	13.123%	$195.205	$195.21	$195.20	$195.20
Purchase #4	$25.65	5.251%	$26.9969	$27.00	$27.00	$27.00
Purchase #5	$50.39	12.263%	$56.5693	$56.57	$56.55	$56.60
Purchase #6	$235.85	6.211%	$250.4986	$250.50	$250.50	$250.50
Purchase #7	$231.32	7.482%	$248.6274	$248.63	$248.65	$248.60
7 purchase totals =	$854.97		$932.7819	$932.79	$932.80	$932.80