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	$148.43	12.118%	$166.4167	$166.42	$166.40	$166.40
Purchase #2	$84.91	6.155%	$90.1362	$90.14	$90.15	$90.10
Purchase #3	$42.63	8.422%	$46.2203	$46.22	$46.20	$46.20
Purchase #4	$220.51	13.114%	$249.4277	$249.43	$249.45	$249.40
Purchase #5	$54.34	8.583%	$59.004	$59.00	$59.00	$59.00
Purchase #6	$151.74	11.442%	$169.1021	$169.10	$169.10	$169.10
Purchase #7	$94.68	10.299%	$104.4311	$104.43	$104.45	$104.40
7 purchase totals =	$797.24		$884.7381	$884.74	$884.75	$884.60