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	$160.96	3.357%	$166.3634	$166.36	$166.35	$166.40
Purchase #2	$10.96	9.751%	$12.0287	$12.03	$12.05	$12.00
Purchase #3	$56.71	9.518%	$62.1077	$62.11	$62.10	$62.10
Purchase #4	$233.35	8.805%	$253.8965	$253.90	$253.90	$253.90
Purchase #5	$245.95	7.725%	$264.9496	$264.95	$264.95	$264.90
Purchase #6	$209.27	13.450%	$237.4168	$237.42	$237.40	$237.40
Purchase #7	$72.34	13.526%	$82.1247	$82.12	$82.10	$82.10
7 purchase totals =	$989.54		$1,078.8874	$1,078.89	$1,078.85	$1,078.80