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	$166.49	8.257%	$180.2371	$180.24	$180.25	$180.20
Purchase #2	$131.97	4.160%	$137.46	$137.46	$137.45	$137.50
Purchase #3	$124.71	9.142%	$136.111	$136.11	$136.10	$136.10
Purchase #4	$153.40	9.680%	$168.2491	$168.25	$168.25	$168.20
Purchase #5	$45.46	6.237%	$48.2953	$48.30	$48.30	$48.30
Purchase #6	$145.47	4.319%	$151.7528	$151.75	$151.75	$151.80
Purchase #7	$96.46	13.218%	$109.2101	$109.21	$109.20	$109.20
7 purchase totals =	$863.96		$931.3154	$931.32	$931.30	$931.30