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	$156.34	8.210%	$169.1755	$169.18	$169.20	$169.20
Purchase #2	$155.90	10.689%	$172.5642	$172.56	$172.55	$172.60
Purchase #3	$249.36	13.271%	$282.4526	$282.45	$282.45	$282.50
Purchase #4	$50.47	10.516%	$55.7774	$55.78	$55.80	$55.80
Purchase #5	$147.92	13.147%	$167.367	$167.37	$167.35	$167.40
Purchase #6	$218.96	4.542%	$228.9052	$228.91	$228.90	$228.90
Purchase #7	$187.36	11.150%	$208.2506	$208.25	$208.25	$208.30
7 purchase totals =	$1,166.31		$1,284.4925	$1,284.50	$1,284.50	$1,284.70