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	$19.67	3.345%	$20.328	$20.33	$20.35	$20.30
Purchase #2	$94.82	10.782%	$105.0435	$105.04	$105.05	$105.00
Purchase #3	$173.35	7.304%	$186.0115	$186.01	$186.00	$186.00
Purchase #4	$152.79	9.812%	$167.7818	$167.78	$167.80	$167.80
Purchase #5	$140.71	6.287%	$149.5564	$149.56	$149.55	$149.60
Purchase #6	$92.60	9.156%	$101.0785	$101.08	$101.10	$101.10
Purchase #7	$113.51	12.373%	$127.5546	$127.55	$127.55	$127.60
7 purchase totals =	$787.45		$857.3543	$857.35	$857.40	$857.40