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	$76.77	12.279%	$86.1966	$86.20	$86.20	$86.20
Purchase #2	$124.48	10.505%	$137.5566	$137.56	$137.55	$137.60
Purchase #3	$40.90	13.122%	$46.2669	$46.27	$46.25	$46.30
Purchase #4	$240.30	11.631%	$268.2493	$268.25	$268.25	$268.20
Purchase #5	$235.54	10.848%	$261.0914	$261.09	$261.10	$261.10
Purchase #6	$134.86	3.343%	$139.3684	$139.37	$139.35	$139.40
Purchase #7	$93.45	7.316%	$100.2868	$100.29	$100.30	$100.30
7 purchase totals =	$946.30		$1,039.0160	$1,039.03	$1,039.00	$1,039.10