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	$140.34	12.462%	$157.8292	$157.83	$157.85	$157.80
Purchase #2	$79.43	13.782%	$90.377	$90.38	$90.40	$90.40
Purchase #3	$89.26	10.382%	$98.527	$98.53	$98.55	$98.50
Purchase #4	$246.30	5.778%	$260.5312	$260.53	$260.55	$260.50
Purchase #5	$136.43	13.329%	$154.6148	$154.61	$154.60	$154.60
Purchase #6	$90.96	4.195%	$94.7758	$94.78	$94.80	$94.80
Purchase #7	$42.27	12.333%	$47.4832	$47.48	$47.50	$47.50
7 purchase totals =	$824.99		$904.1382	$904.14	$904.25	$904.10