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	$119.94	13.518%	$136.1535	$136.15	$136.15	$136.20
Purchase #2	$149.40	12.639%	$168.2827	$168.28	$168.30	$168.30
Purchase #3	$112.35	13.285%	$127.2757	$127.28	$127.30	$127.30
Purchase #4	$81.96	8.254%	$88.725	$88.73	$88.75	$88.70
Purchase #5	$38.76	10.205%	$42.7155	$42.72	$42.70	$42.70
Purchase #6	$171.48	10.758%	$189.9278	$189.93	$189.95	$189.90
Purchase #7	$65.77	3.569%	$68.1173	$68.12	$68.10	$68.10
7 purchase totals =	$739.66		$821.1975	$821.21	$821.25	$821.20