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	$81.27	10.534%	$89.831	$89.83	$89.85	$89.80
Purchase #2	$32.86	5.172%	$34.5595	$34.56	$34.55	$34.60
Purchase #3	$104.37	5.186%	$109.7826	$109.78	$109.80	$109.80
Purchase #4	$197.79	9.558%	$216.6948	$216.69	$216.70	$216.70
Purchase #5	$7.74	4.500%	$8.0883	$8.09	$8.10	$8.10
Purchase #6	$238.88	10.756%	$264.5739	$264.57	$264.55	$264.60
Purchase #7	$8.95	12.350%	$10.0553	$10.06	$10.05	$10.10
7 purchase totals =	$671.86		$733.5854	$733.58	$733.60	$733.70