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	$221.26	12.196%	$248.2449	$248.24	$248.25	$248.20
Purchase #2	$172.62	5.760%	$182.5629	$182.56	$182.55	$182.60
Purchase #3	$52.41	5.660%	$55.3764	$55.38	$55.40	$55.40
Purchase #4	$52.76	5.730%	$55.7831	$55.78	$55.80	$55.80
Purchase #5	$218.53	5.655%	$230.8879	$230.89	$230.90	$230.90
Purchase #6	$107.63	11.792%	$120.3217	$120.32	$120.30	$120.30
Purchase #7	$172.37	7.846%	$185.8942	$185.89	$185.90	$185.90
7 purchase totals =	$997.58		$1,079.0711	$1,079.06	$1,079.10	$1,079.10