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	$157.92	9.791%	$173.3819	$173.38	$173.40	$173.40
Purchase #2	$62.62	4.572%	$65.483	$65.48	$65.50	$65.50
Purchase #3	$58.54	5.715%	$61.8856	$61.89	$61.90	$61.90
Purchase #4	$113.77	13.615%	$129.2598	$129.26	$129.25	$129.30
Purchase #5	$26.48	7.153%	$28.3741	$28.37	$28.35	$28.40
Purchase #6	$129.94	13.801%	$147.873	$147.87	$147.85	$147.90
Purchase #7	$91.44	10.391%	$100.9415	$100.94	$100.95	$100.90
7 purchase totals =	$640.71		$707.1989	$707.19	$707.20	$707.30