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	$166.60	3.466%	$172.3744	$172.37	$172.35	$172.40
Purchase #2	$89.66	12.830%	$101.1634	$101.16	$101.15	$101.20
Purchase #3	$19.44	5.812%	$20.5699	$20.57	$20.55	$20.60
Purchase #4	$64.97	9.623%	$71.2221	$71.22	$71.20	$71.20
Purchase #5	$173.50	5.383%	$182.8395	$182.84	$182.85	$182.80
Purchase #6	$93.31	10.805%	$103.3921	$103.39	$103.40	$103.40
Purchase #7	$161.35	5.567%	$170.3324	$170.33	$170.35	$170.30
7 purchase totals =	$768.83		$821.8938	$821.88	$821.85	$821.90