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	$71.87	11.107%	$79.8526	$79.85	$79.85	$79.90
Purchase #2	$229.41	5.536%	$242.1101	$242.11	$242.10	$242.10
Purchase #3	$204.52	10.299%	$225.5835	$225.58	$225.60	$225.60
Purchase #4	$28.79	3.829%	$29.8924	$29.89	$29.90	$29.90
Purchase #5	$206.30	7.558%	$221.8922	$221.89	$221.90	$221.90
Purchase #6	$134.98	5.106%	$141.8721	$141.87	$141.85	$141.90
Purchase #7	$109.52	13.324%	$124.1124	$124.11	$124.10	$124.10
7 purchase totals =	$985.39		$1,065.3153	$1,065.30	$1,065.30	$1,065.40