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	$91.29	13.273%	$103.4069	$103.41	$103.40	$103.40
Purchase #2	$184.90	3.586%	$191.5305	$191.53	$191.55	$191.50
Purchase #3	$40.80	11.318%	$45.4177	$45.42	$45.40	$45.40
Purchase #4	$127.56	3.614%	$132.17	$132.17	$132.15	$132.20
Purchase #5	$239.49	8.329%	$259.4371	$259.44	$259.45	$259.40
Purchase #6	$140.80	6.274%	$149.6338	$149.63	$149.65	$149.60
Purchase #7	$81.46	9.232%	$88.9804	$88.98	$89.00	$89.00
7 purchase totals =	$906.30		$970.5764	$970.58	$970.60	$970.50