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	$83.60	3.839%	$86.8094	$86.81	$86.80	$86.80
Purchase #2	$180.32	13.409%	$204.4991	$204.50	$204.50	$204.50
Purchase #3	$53.43	11.487%	$59.5675	$59.57	$59.55	$59.60
Purchase #4	$100.58	9.111%	$109.7438	$109.74	$109.75	$109.70
Purchase #5	$57.90	9.108%	$63.1735	$63.17	$63.15	$63.20
Purchase #6	$54.42	4.648%	$56.9494	$56.95	$56.95	$56.90
Purchase #7	$59.92	12.477%	$67.3962	$67.40	$67.40	$67.40
7 purchase totals =	$590.17		$648.1389	$648.14	$648.10	$648.10