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	$81.83	9.165%	$89.3297	$89.33	$89.35	$89.30
Purchase #2	$189.74	5.638%	$200.4375	$200.44	$200.45	$200.40
Purchase #3	$49.27	13.266%	$55.8062	$55.81	$55.80	$55.80
Purchase #4	$207.70	11.268%	$231.1036	$231.10	$231.10	$231.10
Purchase #5	$104.75	4.603%	$109.5716	$109.57	$109.55	$109.60
Purchase #6	$57.54	13.402%	$65.2515	$65.25	$65.25	$65.30
Purchase #7	$117.56	3.745%	$121.9626	$121.96	$121.95	$122.00
7 purchase totals =	$808.39		$873.4627	$873.46	$873.45	$873.50