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	$123.30	6.544%	$131.3688	$131.37	$131.35	$131.40
Purchase #2	$189.35	11.327%	$210.7977	$210.80	$210.80	$210.80
Purchase #3	$174.91	12.267%	$196.3662	$196.37	$196.35	$196.40
Purchase #4	$82.73	9.261%	$90.3916	$90.39	$90.40	$90.40
Purchase #5	$186.50	6.286%	$198.2234	$198.22	$198.20	$198.20
Purchase #6	$44.94	9.135%	$49.0453	$49.05	$49.05	$49.00
Purchase #7	$20.90	4.764%	$21.8957	$21.90	$21.90	$21.90
7 purchase totals =	$822.63		$898.0887	$898.10	$898.05	$898.10