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	$50.96	9.511%	$55.8068	$55.81	$55.80	$55.80
Purchase #2	$50.56	13.457%	$57.3639	$57.36	$57.35	$57.40
Purchase #3	$236.63	13.321%	$268.1515	$268.15	$268.15	$268.20
Purchase #4	$104.30	10.231%	$114.9709	$114.97	$114.95	$115.00
Purchase #5	$33.28	11.710%	$37.1771	$37.18	$37.20	$37.20
Purchase #6	$146.89	13.411%	$166.5894	$166.59	$166.60	$166.60
Purchase #7	$37.43	13.794%	$42.5931	$42.59	$42.60	$42.60
7 purchase totals =	$660.05		$742.6527	$742.65	$742.65	$742.80