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	$77.73	3.189%	$80.2088	$80.21	$80.20	$80.20
Purchase #2	$142.90	13.417%	$162.0729	$162.07	$162.05	$162.10
Purchase #3	$145.60	11.219%	$161.9349	$161.93	$161.95	$161.90
Purchase #4	$43.77	4.664%	$45.8114	$45.81	$45.80	$45.80
Purchase #5	$116.49	9.303%	$127.3271	$127.33	$127.35	$127.30
Purchase #6	$201.55	6.731%	$215.1163	$215.12	$215.10	$215.10
Purchase #7	$72.76	9.211%	$79.4619	$79.46	$79.45	$79.50
7 purchase totals =	$800.80		$871.9333	$871.93	$871.90	$871.90