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	$147.91	8.558%	$160.5681	$160.57	$160.55	$160.60
Purchase #2	$86.53	3.584%	$89.6312	$89.63	$89.65	$89.60
Purchase #3	$80.27	13.792%	$91.3408	$91.34	$91.35	$91.30
Purchase #4	$104.40	4.446%	$109.0416	$109.04	$109.05	$109.00
Purchase #5	$214.59	7.840%	$231.4139	$231.41	$231.40	$231.40
Purchase #6	$219.68	8.398%	$238.1287	$238.13	$238.15	$238.10
Purchase #7	$62.71	3.855%	$65.1275	$65.13	$65.15	$65.10
7 purchase totals =	$916.09		$985.2518	$985.25	$985.30	$985.10