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	$136.34	11.325%	$151.7805	$151.78	$151.80	$151.80
Purchase #2	$200.88	11.373%	$223.7261	$223.73	$223.75	$223.70
Purchase #3	$110.97	11.380%	$123.5984	$123.60	$123.60	$123.60
Purchase #4	$142.80	9.486%	$156.346	$156.35	$156.35	$156.30
Purchase #5	$244.39	13.793%	$278.0987	$278.10	$278.10	$278.10
Purchase #6	$17.61	13.706%	$20.0236	$20.02	$20.00	$20.00
Purchase #7	$127.55	9.174%	$139.2514	$139.25	$139.25	$139.30
7 purchase totals =	$980.54		$1,092.8247	$1,092.83	$1,092.85	$1,092.80