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	$81.44	4.740%	$85.3003	$85.30	$85.30	$85.30
Purchase #2	$18.71	12.573%	$21.0624	$21.06	$21.05	$21.10
Purchase #3	$121.92	7.105%	$130.5824	$130.58	$130.60	$130.60
Purchase #4	$214.64	8.828%	$233.5884	$233.59	$233.60	$233.60
Purchase #5	$130.96	3.475%	$135.5109	$135.51	$135.50	$135.50
Purchase #6	$188.42	5.407%	$198.6079	$198.61	$198.60	$198.60
Purchase #7	$78.42	9.621%	$85.9648	$85.96	$85.95	$86.00
7 purchase totals =	$834.51		$890.6171	$890.61	$890.60	$890.70