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	$152.77	12.154%	$171.3377	$171.34	$171.35	$171.30
Purchase #2	$53.34	5.308%	$56.1713	$56.17	$56.15	$56.20
Purchase #3	$107.79	8.119%	$116.5415	$116.54	$116.55	$116.50
Purchase #4	$235.31	12.264%	$264.1684	$264.17	$264.15	$264.20
Purchase #5	$86.83	6.487%	$92.4627	$92.46	$92.45	$92.50
Purchase #6	$95.46	10.524%	$105.5062	$105.51	$105.50	$105.50
Purchase #7	$224.89	11.680%	$251.1572	$251.16	$251.15	$251.20
7 purchase totals =	$956.39		$1,057.3450	$1,057.35	$1,057.30	$1,057.40