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	$69.72	8.811%	$75.863	$75.86	$75.85	$75.90
Purchase #2	$220.31	3.736%	$228.5408	$228.54	$228.55	$228.50
Purchase #3	$48.61	8.789%	$52.8823	$52.88	$52.90	$52.90
Purchase #4	$83.72	3.340%	$86.5162	$86.52	$86.50	$86.50
Purchase #5	$58.80	13.654%	$66.8286	$66.83	$66.85	$66.80
Purchase #6	$184.67	13.243%	$209.1258	$209.13	$209.15	$209.10
Purchase #7	$106.94	11.690%	$119.4413	$119.44	$119.45	$119.40
7 purchase totals =	$772.77		$839.1980	$839.20	$839.25	$839.10