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	$127.90	13.472%	$145.1307	$145.13	$145.15	$145.10
Purchase #2	$36.37	10.870%	$40.3234	$40.32	$40.30	$40.30
Purchase #3	$202.42	6.861%	$216.308	$216.31	$216.30	$216.30
Purchase #4	$250.63	7.274%	$268.8608	$268.86	$268.85	$268.90
Purchase #5	$248.60	13.490%	$282.1361	$282.14	$282.15	$282.10
Purchase #6	$73.35	4.353%	$76.5429	$76.54	$76.55	$76.50
Purchase #7	$99.59	11.546%	$111.0887	$111.09	$111.10	$111.10
7 purchase totals =	$1,038.86		$1,140.3906	$1,140.39	$1,140.40	$1,140.30