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	$69.46	13.249%	$78.6628	$78.66	$78.65	$78.70
Purchase #2	$18.49	10.811%	$20.489	$20.49	$20.50	$20.50
Purchase #3	$18.73	10.263%	$20.6523	$20.65	$20.65	$20.70
Purchase #4	$160.70	8.532%	$174.4109	$174.41	$174.40	$174.40
Purchase #5	$60.60	7.650%	$65.2359	$65.24	$65.25	$65.20
Purchase #6	$47.35	6.319%	$50.342	$50.34	$50.35	$50.30
Purchase #7	$114.43	3.802%	$118.7806	$118.78	$118.80	$118.80
7 purchase totals =	$489.76		$528.5735	$528.57	$528.60	$528.60