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	$36.26	5.123%	$38.1176	$38.12	$38.10	$38.10
Purchase #2	$64.69	9.561%	$70.875	$70.88	$70.90	$70.90
Purchase #3	$79.52	5.300%	$83.7346	$83.73	$83.75	$83.70
Purchase #4	$95.86	5.423%	$101.0585	$101.06	$101.05	$101.10
Purchase #5	$85.50	10.277%	$94.2868	$94.29	$94.30	$94.30
Purchase #6	$126.39	7.817%	$136.2699	$136.27	$136.25	$136.30
Purchase #7	$153.50	5.833%	$162.4537	$162.45	$162.45	$162.50
7 purchase totals =	$641.72		$686.7961	$686.80	$686.80	$686.90