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	$87.83	3.263%	$90.6959	$90.70	$90.70	$90.70
Purchase #2	$19.86	3.292%	$20.5138	$20.51	$20.50	$20.50
Purchase #3	$69.27	10.198%	$76.3342	$76.33	$76.35	$76.30
Purchase #4	$169.75	9.157%	$185.294	$185.29	$185.30	$185.30
Purchase #5	$6.74	10.632%	$7.4566	$7.46	$7.45	$7.50
Purchase #6	$187.38	12.840%	$211.4396	$211.44	$211.45	$211.40
Purchase #7	$23.99	7.295%	$25.7401	$25.74	$25.75	$25.70
7 purchase totals =	$564.82		$617.4742	$617.47	$617.50	$617.40