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	$81.61	11.471%	$90.9715	$90.97	$90.95	$91.00
Purchase #2	$86.44	4.121%	$90.0022	$90.00	$90.00	$90.00
Purchase #3	$80.30	7.158%	$86.0479	$86.05	$86.05	$86.00
Purchase #4	$42.29	4.603%	$44.2366	$44.24	$44.25	$44.20
Purchase #5	$13.96	7.256%	$14.9729	$14.97	$14.95	$15.00
Purchase #6	$33.63	11.466%	$37.486	$37.49	$37.50	$37.50
Purchase #7	$38.42	3.786%	$39.8746	$39.87	$39.85	$39.90
7 purchase totals =	$376.65		$403.5917	$403.59	$403.55	$403.60