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	$103.40	12.405%	$116.2268	$116.23	$116.25	$116.20
Purchase #2	$57.88	12.761%	$65.2661	$65.27	$65.25	$65.30
Purchase #3	$64.54	4.653%	$67.543	$67.54	$67.55	$67.50
Purchase #4	$210.71	11.202%	$234.3137	$234.31	$234.30	$234.30
Purchase #5	$192.47	12.470%	$216.471	$216.47	$216.45	$216.50
Purchase #6	$187.47	13.358%	$212.5122	$212.51	$212.50	$212.50
Purchase #7	$41.87	3.861%	$43.4866	$43.49	$43.50	$43.50
7 purchase totals =	$858.34		$955.8194	$955.82	$955.80	$955.80