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	$86.37	4.198%	$89.9958	$90.00	$90.00	$90.00
Purchase #2	$241.79	11.424%	$269.4121	$269.41	$269.40	$269.40
Purchase #3	$36.67	10.616%	$40.5629	$40.56	$40.55	$40.60
Purchase #4	$117.93	5.872%	$124.8548	$124.85	$124.85	$124.90
Purchase #5	$103.62	13.351%	$117.4543	$117.45	$117.45	$117.50
Purchase #6	$209.90	6.443%	$223.4239	$223.42	$223.40	$223.40
Purchase #7	$95.50	9.696%	$104.7597	$104.76	$104.75	$104.80
7 purchase totals =	$891.78		$970.4635	$970.45	$970.40	$970.60