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	$11.56	3.824%	$12.0021	$12.00	$12.00	$12.00
Purchase #2	$146.73	4.869%	$153.8743	$153.87	$153.85	$153.90
Purchase #3	$75.54	3.330%	$78.0555	$78.06	$78.05	$78.10
Purchase #4	$182.66	3.788%	$189.5792	$189.58	$189.60	$189.60
Purchase #5	$174.35	4.520%	$182.2306	$182.23	$182.25	$182.20
Purchase #6	$151.31	10.810%	$167.6666	$167.67	$167.65	$167.70
Purchase #7	$147.78	7.793%	$159.2965	$159.30	$159.30	$159.30
7 purchase totals =	$889.93		$942.7048	$942.71	$942.70	$942.80