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	$179.45	10.542%	$198.3676	$198.37	$198.35	$198.40
Purchase #2	$90.54	10.785%	$100.3047	$100.30	$100.30	$100.30
Purchase #3	$48.46	4.168%	$50.4798	$50.48	$50.50	$50.50
Purchase #4	$99.69	5.132%	$104.8061	$104.81	$104.80	$104.80
Purchase #5	$160.64	9.422%	$175.7755	$175.78	$175.80	$175.80
Purchase #6	$133.47	6.816%	$142.5673	$142.57	$142.55	$142.60
Purchase #7	$155.38	7.552%	$167.1143	$167.11	$167.10	$167.10
7 purchase totals =	$867.63		$939.4153	$939.42	$939.40	$939.50