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	$214.26	12.380%	$240.7854	$240.79	$240.80	$240.80
Purchase #2	$108.67	6.579%	$115.8194	$115.82	$115.80	$115.80
Purchase #3	$92.33	12.492%	$103.8639	$103.86	$103.85	$103.90
Purchase #4	$152.75	8.694%	$166.0301	$166.03	$166.05	$166.00
Purchase #5	$195.41	10.798%	$216.5104	$216.51	$216.50	$216.50
Purchase #6	$73.76	6.466%	$78.5293	$78.53	$78.55	$78.50
Purchase #7	$191.41	9.494%	$209.5825	$209.58	$209.60	$209.60
7 purchase totals =	$1,028.59		$1,131.1210	$1,131.12	$1,131.15	$1,131.10