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	$37.53	8.211%	$40.6116	$40.61	$40.60	$40.60
Purchase #2	$127.34	9.242%	$139.1088	$139.11	$139.10	$139.10
Purchase #3	$45.68	10.640%	$50.5404	$50.54	$50.55	$50.50
Purchase #4	$35.70	13.741%	$40.6055	$40.61	$40.60	$40.60
Purchase #5	$245.74	10.293%	$271.034	$271.03	$271.05	$271.00
Purchase #6	$178.60	9.241%	$195.1044	$195.10	$195.10	$195.10
Purchase #7	$76.44	4.143%	$79.6069	$79.61	$79.60	$79.60
7 purchase totals =	$747.03		$816.6116	$816.61	$816.60	$816.50