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	$246.26	11.406%	$274.3484	$274.35	$274.35	$274.30
Purchase #2	$28.98	4.591%	$30.3105	$30.31	$30.30	$30.30
Purchase #3	$150.92	10.398%	$166.6127	$166.61	$166.60	$166.60
Purchase #4	$155.72	12.121%	$174.5948	$174.59	$174.60	$174.60
Purchase #5	$212.61	13.662%	$241.6568	$241.66	$241.65	$241.70
Purchase #6	$162.25	4.271%	$169.1797	$169.18	$169.20	$169.20
Purchase #7	$54.71	9.483%	$59.8981	$59.90	$59.90	$59.90
7 purchase totals =	$1,011.45		$1,116.6010	$1,116.60	$1,116.60	$1,116.60