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	$65.96	9.585%	$72.2823	$72.28	$72.30	$72.30
Purchase #2	$6.34	12.269%	$7.1179	$7.12	$7.10	$7.10
Purchase #3	$106.49	13.483%	$120.848	$120.85	$120.85	$120.80
Purchase #4	$164.98	10.183%	$181.7799	$181.78	$181.80	$181.80
Purchase #5	$70.87	13.722%	$80.5948	$80.59	$80.60	$80.60
Purchase #6	$62.95	13.395%	$71.3822	$71.38	$71.40	$71.40
Purchase #7	$171.58	13.168%	$194.1737	$194.17	$194.15	$194.20
7 purchase totals =	$649.17		$728.1788	$728.17	$728.20	$728.20