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	$143.29	6.317%	$152.3416	$152.34	$152.35	$152.30
Purchase #2	$124.86	10.872%	$138.4348	$138.43	$138.45	$138.40
Purchase #3	$37.47	13.308%	$42.4565	$42.46	$42.45	$42.50
Purchase #4	$57.79	4.570%	$60.431	$60.43	$60.45	$60.40
Purchase #5	$94.96	4.532%	$99.2636	$99.26	$99.25	$99.30
Purchase #6	$53.83	6.564%	$57.3634	$57.36	$57.35	$57.40
Purchase #7	$107.95	9.842%	$118.5744	$118.57	$118.55	$118.60
7 purchase totals =	$620.15		$668.8653	$668.85	$668.85	$668.90