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	$82.42	11.479%	$91.881	$91.88	$91.90	$91.90
Purchase #2	$151.90	9.645%	$166.5508	$166.55	$166.55	$166.60
Purchase #3	$189.45	7.633%	$203.9107	$203.91	$203.90	$203.90
Purchase #4	$59.83	11.345%	$66.6177	$66.62	$66.60	$66.60
Purchase #5	$143.30	9.150%	$156.412	$156.41	$156.40	$156.40
Purchase #6	$208.41	5.769%	$220.4332	$220.43	$220.45	$220.40
Purchase #7	$143.61	6.174%	$152.4765	$152.48	$152.50	$152.50
7 purchase totals =	$978.92		$1,058.2819	$1,058.28	$1,058.30	$1,058.30