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	$11.84	6.292%	$12.585	$12.59	$12.60	$12.60
Purchase #2	$54.96	13.549%	$62.4065	$62.41	$62.40	$62.40
Purchase #3	$54.63	12.770%	$61.6063	$61.61	$61.60	$61.60
Purchase #4	$45.96	10.558%	$50.8125	$50.81	$50.80	$50.80
Purchase #5	$248.34	10.284%	$273.8793	$273.88	$273.90	$273.90
Purchase #6	$81.66	10.381%	$90.1371	$90.14	$90.15	$90.10
Purchase #7	$79.58	4.758%	$83.3664	$83.37	$83.35	$83.40
7 purchase totals =	$576.97		$634.7931	$634.81	$634.80	$634.80