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	$89.90	12.851%	$101.453	$101.45	$101.45	$101.50
Purchase #2	$136.59	8.562%	$148.2848	$148.28	$148.30	$148.30
Purchase #3	$214.93	12.672%	$242.1659	$242.17	$242.15	$242.20
Purchase #4	$196.74	13.283%	$222.873	$222.87	$222.85	$222.90
Purchase #5	$129.47	7.367%	$139.0081	$139.01	$139.00	$139.00
Purchase #6	$225.72	7.478%	$242.5993	$242.60	$242.60	$242.60
Purchase #7	$46.25	13.402%	$52.4484	$52.45	$52.45	$52.40
7 purchase totals =	$1,039.60		$1,148.8325	$1,148.83	$1,148.80	$1,148.90