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	$123.89	10.433%	$136.8154	$136.82	$136.80	$136.80
Purchase #2	$149.96	6.253%	$159.337	$159.34	$159.35	$159.30
Purchase #3	$242.77	13.470%	$275.4711	$275.47	$275.45	$275.50
Purchase #4	$222.26	9.321%	$242.9769	$242.98	$243.00	$243.00
Purchase #5	$209.80	9.439%	$229.603	$229.60	$229.60	$229.60
Purchase #6	$244.31	4.512%	$255.3333	$255.33	$255.35	$255.30
Purchase #7	$41.46	4.648%	$43.3871	$43.39	$43.40	$43.40
7 purchase totals =	$1,234.45		$1,342.9238	$1,342.93	$1,342.95	$1,342.90