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	$134.73	9.538%	$147.5805	$147.58	$147.60	$147.60
Purchase #2	$33.42	7.426%	$35.9018	$35.90	$35.90	$35.90
Purchase #3	$20.30	8.193%	$21.9632	$21.96	$21.95	$22.00
Purchase #4	$90.29	4.150%	$94.037	$94.04	$94.05	$94.00
Purchase #5	$160.29	7.409%	$172.1659	$172.17	$172.15	$172.20
Purchase #6	$105.88	3.802%	$109.9056	$109.91	$109.90	$109.90
Purchase #7	$250.41	4.169%	$260.8496	$260.85	$260.85	$260.80
7 purchase totals =	$795.32		$842.4036	$842.41	$842.40	$842.40