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	$83.51	8.150%	$90.3161	$90.32	$90.30	$90.30
Purchase #2	$246.90	5.692%	$260.9535	$260.95	$260.95	$261.00
Purchase #3	$165.38	13.342%	$187.445	$187.45	$187.45	$187.40
Purchase #4	$69.44	9.171%	$75.8083	$75.81	$75.80	$75.80
Purchase #5	$38.79	9.235%	$42.3723	$42.37	$42.35	$42.40
Purchase #6	$250.90	7.335%	$269.3035	$269.30	$269.30	$269.30
Purchase #7	$121.46	8.345%	$131.5958	$131.60	$131.60	$131.60
7 purchase totals =	$976.38		$1,057.7945	$1,057.80	$1,057.75	$1,057.80