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	$16.73	10.409%	$18.4714	$18.47	$18.45	$18.50
Purchase #2	$197.71	13.505%	$224.4107	$224.41	$224.40	$224.40
Purchase #3	$104.43	5.844%	$110.5329	$110.53	$110.55	$110.50
Purchase #4	$93.63	10.365%	$103.3347	$103.33	$103.35	$103.30
Purchase #5	$201.73	5.162%	$212.1433	$212.14	$212.15	$212.10
Purchase #6	$219.48	5.274%	$231.0554	$231.06	$231.05	$231.10
Purchase #7	$171.83	8.120%	$185.7826	$185.78	$185.80	$185.80
7 purchase totals =	$1,005.54		$1,085.7310	$1,085.72	$1,085.75	$1,085.70