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	$99.54	5.794%	$105.3073	$105.31	$105.30	$105.30
Purchase #2	$98.28	11.263%	$109.3493	$109.35	$109.35	$109.30
Purchase #3	$59.39	12.387%	$66.7466	$66.75	$66.75	$66.70
Purchase #4	$205.99	11.196%	$229.0526	$229.05	$229.05	$229.10
Purchase #5	$47.39	8.770%	$51.5461	$51.55	$51.55	$51.50
Purchase #6	$13.87	10.261%	$15.2932	$15.29	$15.30	$15.30
Purchase #7	$71.45	12.802%	$80.597	$80.60	$80.60	$80.60
7 purchase totals =	$595.91		$657.8921	$657.90	$657.90	$657.80