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	$29.34	13.114%	$33.1876	$33.19	$33.20	$33.20
Purchase #2	$137.73	6.448%	$146.6108	$146.61	$146.60	$146.60
Purchase #3	$73.61	5.695%	$77.8021	$77.80	$77.80	$77.80
Purchase #4	$45.55	13.252%	$51.5863	$51.59	$51.60	$51.60
Purchase #5	$34.97	6.285%	$37.1679	$37.17	$37.15	$37.20
Purchase #6	$59.32	13.539%	$67.3513	$67.35	$67.35	$67.40
Purchase #7	$19.68	12.478%	$22.1357	$22.14	$22.15	$22.10
7 purchase totals =	$400.20		$435.8417	$435.85	$435.85	$435.90