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	$80.40	12.292%	$90.2828	$90.28	$90.30	$90.30
Purchase #2	$15.79	7.372%	$16.954	$16.95	$16.95	$17.00
Purchase #3	$81.57	9.598%	$89.3991	$89.40	$89.40	$89.40
Purchase #4	$231.31	10.845%	$256.3956	$256.40	$256.40	$256.40
Purchase #5	$153.93	5.188%	$161.9159	$161.92	$161.90	$161.90
Purchase #6	$162.26	7.427%	$174.3111	$174.31	$174.30	$174.30
Purchase #7	$86.39	5.304%	$90.9721	$90.97	$90.95	$91.00
7 purchase totals =	$811.65		$880.2306	$880.23	$880.20	$880.30