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	$88.86	13.470%	$100.8294	$100.83	$100.85	$100.80
Purchase #2	$43.83	4.481%	$45.794	$45.79	$45.80	$45.80
Purchase #3	$71.95	4.719%	$75.3453	$75.35	$75.35	$75.30
Purchase #4	$32.26	9.656%	$35.375	$35.38	$35.40	$35.40
Purchase #5	$232.66	5.734%	$246.0007	$246.00	$246.00	$246.00
Purchase #6	$215.47	13.511%	$244.5822	$244.58	$244.60	$244.60
Purchase #7	$233.47	13.222%	$264.3394	$264.34	$264.35	$264.30
7 purchase totals =	$918.50		$1,012.2660	$1,012.27	$1,012.35	$1,012.20