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	$174.91	7.175%	$187.4598	$187.46	$187.45	$187.50
Purchase #2	$46.69	3.652%	$48.3951	$48.40	$48.40	$48.40
Purchase #3	$48.83	11.725%	$54.5553	$54.56	$54.55	$54.60
Purchase #4	$63.74	3.280%	$65.8307	$65.83	$65.85	$65.80
Purchase #5	$73.76	12.753%	$83.1666	$83.17	$83.15	$83.20
Purchase #6	$87.28	3.238%	$90.1061	$90.11	$90.10	$90.10
Purchase #7	$238.40	4.699%	$249.6024	$249.60	$249.60	$249.60
7 purchase totals =	$733.61		$779.1160	$779.13	$779.10	$779.20