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	$79.81	8.159%	$86.3217	$86.32	$86.30	$86.30
Purchase #2	$81.38	9.370%	$89.0053	$89.01	$89.00	$89.00
Purchase #3	$46.75	12.482%	$52.5853	$52.59	$52.60	$52.60
Purchase #4	$101.67	12.856%	$114.7407	$114.74	$114.75	$114.70
Purchase #5	$58.33	13.739%	$66.344	$66.34	$66.35	$66.30
Purchase #6	$176.31	7.265%	$189.1189	$189.12	$189.10	$189.10
Purchase #7	$225.62	6.530%	$240.353	$240.35	$240.35	$240.40
7 purchase totals =	$769.87		$838.4689	$838.47	$838.45	$838.40