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	$17.42	6.574%	$18.5652	$18.57	$18.55	$18.60
Purchase #2	$6.73	9.126%	$7.3442	$7.34	$7.35	$7.30
Purchase #3	$109.85	10.303%	$121.1678	$121.17	$121.15	$121.20
Purchase #4	$47.25	5.402%	$49.8024	$49.80	$49.80	$49.80
Purchase #5	$42.81	6.219%	$45.4724	$45.47	$45.45	$45.50
Purchase #6	$58.54	6.691%	$62.4569	$62.46	$62.45	$62.50
Purchase #7	$68.72	4.363%	$71.7183	$71.72	$71.70	$71.70
7 purchase totals =	$351.32		$376.5272	$376.53	$376.45	$376.60