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	$69.57	4.676%	$72.8231	$72.82	$72.80	$72.80
Purchase #2	$35.53	12.841%	$40.0924	$40.09	$40.10	$40.10
Purchase #3	$206.63	4.264%	$215.4407	$215.44	$215.45	$215.40
Purchase #4	$233.61	3.375%	$241.4943	$241.49	$241.50	$241.50
Purchase #5	$242.62	11.271%	$269.9657	$269.97	$269.95	$270.00
Purchase #6	$72.51	10.175%	$79.8879	$79.89	$79.90	$79.90
Purchase #7	$17.77	3.365%	$18.368	$18.37	$18.35	$18.40
7 purchase totals =	$878.24		$938.0721	$938.07	$938.05	$938.10