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	$95.42	4.816%	$100.0154	$100.02	$100.00	$100.00
Purchase #2	$53.35	12.357%	$59.9425	$59.94	$59.95	$59.90
Purchase #3	$196.85	12.444%	$221.346	$221.35	$221.35	$221.30
Purchase #4	$26.67	6.664%	$28.4473	$28.45	$28.45	$28.40
Purchase #5	$31.31	7.502%	$33.6589	$33.66	$33.65	$33.70
Purchase #6	$139.91	13.465%	$158.7489	$158.75	$158.75	$158.70
Purchase #7	$123.45	8.267%	$133.6556	$133.66	$133.65	$133.70
7 purchase totals =	$666.96		$735.8146	$735.83	$735.80	$735.70