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	$116.63	10.538%	$128.9205	$128.92	$128.90	$128.90
Purchase #2	$35.96	3.738%	$37.3042	$37.30	$37.30	$37.30
Purchase #3	$27.73	13.420%	$31.4514	$31.45	$31.45	$31.50
Purchase #4	$138.33	12.346%	$155.4082	$155.41	$155.40	$155.40
Purchase #5	$95.27	5.118%	$100.1459	$100.15	$100.15	$100.10
Purchase #6	$83.76	7.645%	$90.1635	$90.16	$90.15	$90.20
Purchase #7	$63.71	9.252%	$69.6044	$69.60	$69.60	$69.60
7 purchase totals =	$561.39		$612.9981	$612.99	$612.95	$613.00