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	$97.70	6.181%	$103.7388	$103.74	$103.75	$103.70
Purchase #2	$31.26	8.806%	$34.0128	$34.01	$34.00	$34.00
Purchase #3	$134.34	3.698%	$139.3079	$139.31	$139.30	$139.30
Purchase #4	$72.78	7.573%	$78.2916	$78.29	$78.30	$78.30
Purchase #5	$237.25	12.786%	$267.5848	$267.58	$267.60	$267.60
Purchase #6	$73.42	13.580%	$83.3904	$83.39	$83.40	$83.40
Purchase #7	$92.27	8.799%	$100.3888	$100.39	$100.40	$100.40
7 purchase totals =	$739.02		$806.7151	$806.71	$806.75	$806.70