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	$30.82	6.356%	$32.7789	$32.78	$32.80	$32.80
Purchase #2	$128.82	13.597%	$146.3357	$146.34	$146.35	$146.30
Purchase #3	$40.70	5.774%	$43.05	$43.05	$43.05	$43.10
Purchase #4	$50.99	11.132%	$56.6662	$56.67	$56.65	$56.70
Purchase #5	$222.32	8.185%	$240.5169	$240.52	$240.50	$240.50
Purchase #6	$201.62	7.448%	$216.6367	$216.64	$216.65	$216.60
Purchase #7	$160.60	4.521%	$167.8607	$167.86	$167.85	$167.90
7 purchase totals =	$835.87		$903.8451	$903.86	$903.85	$903.90