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	$129.31	10.171%	$142.4621	$142.46	$142.45	$142.50
Purchase #2	$168.33	3.476%	$174.1812	$174.18	$174.20	$174.20
Purchase #3	$116.81	8.866%	$127.1664	$127.17	$127.15	$127.20
Purchase #4	$123.98	3.326%	$128.1036	$128.10	$128.10	$128.10
Purchase #5	$26.68	9.167%	$29.1258	$29.13	$29.15	$29.10
Purchase #6	$160.63	12.253%	$180.312	$180.31	$180.30	$180.30
Purchase #7	$50.67	8.265%	$54.8579	$54.86	$54.85	$54.90
7 purchase totals =	$776.41		$836.2090	$836.21	$836.20	$836.30