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	$110.60	11.326%	$123.1266	$123.13	$123.15	$123.10
Purchase #2	$31.50	7.211%	$33.7715	$33.77	$33.75	$33.80
Purchase #3	$146.52	12.523%	$164.8687	$164.87	$164.85	$164.90
Purchase #4	$213.52	9.696%	$234.2229	$234.22	$234.20	$234.20
Purchase #5	$222.83	11.482%	$248.4153	$248.42	$248.40	$248.40
Purchase #6	$29.89	11.121%	$33.2141	$33.21	$33.20	$33.20
Purchase #7	$221.57	12.373%	$248.9849	$248.98	$249.00	$249.00
7 purchase totals =	$976.43		$1,086.6040	$1,086.60	$1,086.55	$1,086.60