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	$18.77	6.833%	$20.0526	$20.05	$20.05	$20.10
Purchase #2	$67.41	11.103%	$74.8945	$74.89	$74.90	$74.90
Purchase #3	$189.78	5.393%	$200.0148	$200.01	$200.00	$200.00
Purchase #4	$23.64	4.873%	$24.792	$24.79	$24.80	$24.80
Purchase #5	$222.26	6.597%	$236.9225	$236.92	$236.90	$236.90
Purchase #6	$85.27	11.348%	$94.9464	$94.95	$94.95	$94.90
Purchase #7	$86.52	3.598%	$89.633	$89.63	$89.65	$89.60
7 purchase totals =	$693.65		$741.2558	$741.24	$741.25	$741.20