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	$160.33	7.258%	$171.9668	$171.97	$171.95	$172.00
Purchase #2	$36.69	11.404%	$40.8741	$40.87	$40.85	$40.90
Purchase #3	$226.67	12.812%	$255.711	$255.71	$255.70	$255.70
Purchase #4	$157.34	6.809%	$168.0533	$168.05	$168.05	$168.10
Purchase #5	$141.25	8.810%	$153.6941	$153.69	$153.70	$153.70
Purchase #6	$143.86	3.241%	$148.5225	$148.52	$148.50	$148.50
Purchase #7	$33.34	7.800%	$35.9405	$35.94	$35.95	$35.90
7 purchase totals =	$899.48		$974.7623	$974.75	$974.70	$974.80