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	$201.54	13.148%	$228.0385	$228.04	$228.05	$228.00
Purchase #2	$100.45	4.765%	$105.2364	$105.24	$105.25	$105.20
Purchase #3	$117.63	4.564%	$122.9986	$123.00	$123.00	$123.00
Purchase #4	$10.98	3.799%	$11.3971	$11.40	$11.40	$11.40
Purchase #5	$165.68	4.366%	$172.9136	$172.91	$172.90	$172.90
Purchase #6	$35.77	13.349%	$40.5449	$40.54	$40.55	$40.50
Purchase #7	$177.33	6.615%	$189.0604	$189.06	$189.05	$189.10
7 purchase totals =	$809.38		$870.1895	$870.19	$870.20	$870.10