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	$171.80	10.740%	$190.2513	$190.25	$190.25	$190.30
Purchase #2	$181.93	3.189%	$187.7317	$187.73	$187.75	$187.70
Purchase #3	$46.30	8.104%	$50.0522	$50.05	$50.05	$50.10
Purchase #4	$147.88	4.149%	$154.0155	$154.02	$154.00	$154.00
Purchase #5	$89.48	7.117%	$95.8483	$95.85	$95.85	$95.80
Purchase #6	$50.75	5.298%	$53.4387	$53.44	$53.45	$53.40
Purchase #7	$94.96	3.484%	$98.2684	$98.27	$98.25	$98.30
7 purchase totals =	$783.10		$829.6061	$829.61	$829.60	$829.60