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	$63.59	11.471%	$70.8844	$70.88	$70.90	$70.90
Purchase #2	$52.93	4.637%	$55.3844	$55.38	$55.40	$55.40
Purchase #3	$155.31	6.801%	$165.8726	$165.87	$165.85	$165.90
Purchase #4	$217.59	3.262%	$224.6878	$224.69	$224.70	$224.70
Purchase #5	$233.41	9.742%	$256.1488	$256.15	$256.15	$256.10
Purchase #6	$51.95	13.118%	$58.7648	$58.76	$58.75	$58.80
Purchase #7	$24.76	9.762%	$27.1771	$27.18	$27.20	$27.20
7 purchase totals =	$799.54		$858.9199	$858.91	$858.95	$859.00