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	$100.84	10.383%	$111.3102	$111.31	$111.30	$111.30
Purchase #2	$221.72	8.629%	$240.8522	$240.85	$240.85	$240.90
Purchase #3	$123.68	6.656%	$131.9121	$131.91	$131.90	$131.90
Purchase #4	$169.63	10.257%	$187.0289	$187.03	$187.05	$187.00
Purchase #5	$34.59	9.356%	$37.8262	$37.83	$37.85	$37.80
Purchase #6	$153.46	5.435%	$161.8006	$161.80	$161.80	$161.80
Purchase #7	$249.96	3.404%	$258.4686	$258.47	$258.45	$258.50
7 purchase totals =	$1,053.88		$1,129.1988	$1,129.20	$1,129.20	$1,129.20