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	$117.25	5.224%	$123.3751	$123.38	$123.40	$123.40
Purchase #2	$147.97	5.374%	$155.9219	$155.92	$155.90	$155.90
Purchase #3	$85.51	7.824%	$92.2003	$92.20	$92.20	$92.20
Purchase #4	$137.47	6.860%	$146.9004	$146.90	$146.90	$146.90
Purchase #5	$34.89	4.556%	$36.4796	$36.48	$36.50	$36.50
Purchase #6	$134.55	13.408%	$152.5905	$152.59	$152.60	$152.60
Purchase #7	$238.90	11.472%	$266.3066	$266.31	$266.30	$266.30
7 purchase totals =	$896.54		$973.7744	$973.78	$973.80	$973.80