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	$109.85	6.387%	$116.8661	$116.87	$116.85	$116.90
Purchase #2	$50.36	5.648%	$53.2043	$53.20	$53.20	$53.20
Purchase #3	$180.91	7.665%	$194.7768	$194.78	$194.80	$194.80
Purchase #4	$172.53	10.825%	$191.2064	$191.21	$191.20	$191.20
Purchase #5	$38.76	6.705%	$41.3589	$41.36	$41.35	$41.40
Purchase #6	$148.46	6.685%	$158.3846	$158.38	$158.40	$158.40
Purchase #7	$219.74	10.789%	$243.4477	$243.45	$243.45	$243.40
7 purchase totals =	$920.61		$999.2448	$999.25	$999.25	$999.30