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	$80.68	13.148%	$91.2878	$91.29	$91.30	$91.30
Purchase #2	$109.83	12.290%	$123.3281	$123.33	$123.35	$123.30
Purchase #3	$67.61	5.404%	$71.2636	$71.26	$71.25	$71.30
Purchase #4	$59.58	7.184%	$63.8602	$63.86	$63.85	$63.90
Purchase #5	$44.80	4.516%	$46.8232	$46.82	$46.80	$46.80
Purchase #6	$15.64	11.605%	$17.455	$17.46	$17.45	$17.50
Purchase #7	$30.64	12.273%	$34.4004	$34.40	$34.40	$34.40
7 purchase totals =	$408.78		$448.4183	$448.42	$448.40	$448.50