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	$249.92	7.732%	$269.2438	$269.24	$269.25	$269.20
Purchase #2	$55.76	11.441%	$62.1395	$62.14	$62.15	$62.10
Purchase #3	$82.89	13.143%	$93.7842	$93.78	$93.80	$93.80
Purchase #4	$248.65	4.340%	$259.4414	$259.44	$259.45	$259.40
Purchase #5	$116.61	10.679%	$129.0628	$129.06	$129.05	$129.10
Purchase #6	$119.61	7.643%	$128.7518	$128.75	$128.75	$128.80
Purchase #7	$86.86	4.557%	$90.8182	$90.82	$90.80	$90.80
7 purchase totals =	$960.30		$1,033.2417	$1,033.23	$1,033.25	$1,033.20