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	$64.48	9.270%	$70.4573	$70.46	$70.45	$70.50
Purchase #2	$17.55	3.280%	$18.1256	$18.13	$18.15	$18.10
Purchase #3	$54.82	3.109%	$56.5244	$56.52	$56.50	$56.50
Purchase #4	$217.26	11.806%	$242.9097	$242.91	$242.90	$242.90
Purchase #5	$220.62	8.126%	$238.5476	$238.55	$238.55	$238.50
Purchase #6	$154.71	10.571%	$171.0644	$171.06	$171.05	$171.10
Purchase #7	$136.83	7.232%	$146.7255	$146.73	$146.75	$146.70
7 purchase totals =	$866.27		$944.3545	$944.36	$944.35	$944.30