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	$199.96	12.560%	$225.075	$225.08	$225.10	$225.10
Purchase #2	$156.92	6.346%	$166.8781	$166.88	$166.90	$166.90
Purchase #3	$130.93	11.632%	$146.1598	$146.16	$146.15	$146.20
Purchase #4	$56.52	12.461%	$63.563	$63.56	$63.55	$63.60
Purchase #5	$216.26	8.241%	$234.082	$234.08	$234.10	$234.10
Purchase #6	$131.94	5.623%	$139.359	$139.36	$139.35	$139.40
Purchase #7	$99.25	5.850%	$105.0561	$105.06	$105.05	$105.10
7 purchase totals =	$991.78		$1,080.1730	$1,080.18	$1,080.20	$1,080.40