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	$122.66	11.765%	$137.0909	$137.09	$137.10	$137.10
Purchase #2	$44.33	10.115%	$48.814	$48.81	$48.80	$48.80
Purchase #3	$195.90	4.707%	$205.121	$205.12	$205.10	$205.10
Purchase #4	$82.83	8.340%	$89.738	$89.74	$89.75	$89.70
Purchase #5	$52.96	12.272%	$59.4593	$59.46	$59.45	$59.50
Purchase #6	$150.89	10.273%	$166.3909	$166.39	$166.40	$166.40
Purchase #7	$112.70	9.188%	$123.0549	$123.05	$123.05	$123.10
7 purchase totals =	$762.27		$829.6690	$829.66	$829.65	$829.70