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	$147.94	11.768%	$165.3496	$165.35	$165.35	$165.30
Purchase #2	$74.52	8.255%	$80.6716	$80.67	$80.65	$80.70
Purchase #3	$194.88	10.438%	$215.2216	$215.22	$215.20	$215.20
Purchase #4	$158.35	12.659%	$178.3955	$178.40	$178.40	$178.40
Purchase #5	$46.36	9.523%	$50.7749	$50.77	$50.75	$50.80
Purchase #6	$66.31	7.605%	$71.3529	$71.35	$71.35	$71.40
Purchase #7	$95.98	3.281%	$99.1291	$99.13	$99.15	$99.10
7 purchase totals =	$784.34		$860.8952	$860.89	$860.85	$860.90