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	$52.79	12.471%	$59.3734	$59.37	$59.35	$59.40
Purchase #2	$227.85	7.619%	$245.2099	$245.21	$245.20	$245.20
Purchase #3	$147.91	9.677%	$162.2233	$162.22	$162.20	$162.20
Purchase #4	$222.68	12.649%	$250.8468	$250.85	$250.85	$250.80
Purchase #5	$105.73	13.190%	$119.6758	$119.68	$119.70	$119.70
Purchase #6	$10.52	11.706%	$11.7515	$11.75	$11.75	$11.80
Purchase #7	$122.67	5.581%	$129.5162	$129.52	$129.50	$129.50
7 purchase totals =	$890.15		$978.5969	$978.60	$978.55	$978.60