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	$159.47	4.585%	$166.7817	$166.78	$166.80	$166.80
Purchase #2	$98.97	12.516%	$111.3571	$111.36	$111.35	$111.40
Purchase #3	$171.38	9.321%	$187.3543	$187.35	$187.35	$187.40
Purchase #4	$137.90	4.808%	$144.5302	$144.53	$144.55	$144.50
Purchase #5	$150.54	6.659%	$160.5645	$160.56	$160.55	$160.60
Purchase #6	$221.50	10.231%	$244.1617	$244.16	$244.15	$244.20
Purchase #7	$127.42	9.481%	$139.5007	$139.50	$139.50	$139.50
7 purchase totals =	$1,067.18		$1,154.2502	$1,154.24	$1,154.25	$1,154.40