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	$96.96	6.762%	$103.5164	$103.52	$103.50	$103.50
Purchase #2	$94.91	11.868%	$106.1739	$106.17	$106.15	$106.20
Purchase #3	$128.96	13.497%	$146.3657	$146.37	$146.35	$146.40
Purchase #4	$127.50	8.556%	$138.4089	$138.41	$138.40	$138.40
Purchase #5	$138.90	12.308%	$155.9958	$156.00	$156.00	$156.00
Purchase #6	$73.39	7.386%	$78.8106	$78.81	$78.80	$78.80
Purchase #7	$97.83	3.753%	$101.5016	$101.50	$101.50	$101.50
7 purchase totals =	$758.45		$830.7729	$830.78	$830.70	$830.80