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	$141.61	3.421%	$146.4545	$146.45	$146.45	$146.50
Purchase #2	$150.30	9.714%	$164.9001	$164.90	$164.90	$164.90
Purchase #3	$81.60	8.779%	$88.7637	$88.76	$88.75	$88.80
Purchase #4	$44.99	4.691%	$47.1005	$47.10	$47.10	$47.10
Purchase #5	$125.55	9.600%	$137.6028	$137.60	$137.60	$137.60
Purchase #6	$68.95	13.485%	$78.2479	$78.25	$78.25	$78.20
Purchase #7	$171.72	8.195%	$185.7925	$185.79	$185.80	$185.80
7 purchase totals =	$784.72		$848.8620	$848.85	$848.85	$848.90