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	$209.83	8.817%	$228.3307	$228.33	$228.35	$228.30
Purchase #2	$53.70	4.655%	$56.1997	$56.20	$56.20	$56.20
Purchase #3	$235.78	7.632%	$253.7747	$253.77	$253.75	$253.80
Purchase #4	$85.62	4.563%	$89.5268	$89.53	$89.55	$89.50
Purchase #5	$163.62	3.641%	$169.5774	$169.58	$169.60	$169.60
Purchase #6	$55.42	7.686%	$59.6796	$59.68	$59.70	$59.70
Purchase #7	$249.86	5.868%	$264.5218	$264.52	$264.50	$264.50
7 purchase totals =	$1,053.83		$1,121.6107	$1,121.61	$1,121.65	$1,121.60