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	$32.52	8.668%	$35.3388	$35.34	$35.35	$35.30
Purchase #2	$78.31	6.664%	$83.5286	$83.53	$83.55	$83.50
Purchase #3	$91.51	8.826%	$99.5867	$99.59	$99.60	$99.60
Purchase #4	$77.97	8.351%	$84.4813	$84.48	$84.50	$84.50
Purchase #5	$97.88	9.606%	$107.2824	$107.28	$107.30	$107.30
Purchase #6	$80.73	9.405%	$88.3227	$88.32	$88.30	$88.30
Purchase #7	$82.56	9.182%	$90.1407	$90.14	$90.15	$90.10
7 purchase totals =	$541.48		$588.6812	$588.68	$588.75	$588.60