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	$110.38	12.202%	$123.8486	$123.85	$123.85	$123.80
Purchase #2	$154.56	11.175%	$171.8321	$171.83	$171.85	$171.80
Purchase #3	$49.95	5.123%	$52.5089	$52.51	$52.50	$52.50
Purchase #4	$198.77	11.608%	$221.8432	$221.84	$221.85	$221.80
Purchase #5	$206.93	10.435%	$228.5231	$228.52	$228.50	$228.50
Purchase #6	$14.76	12.441%	$16.5963	$16.60	$16.60	$16.60
Purchase #7	$17.76	12.648%	$20.0063	$20.01	$20.00	$20.00
7 purchase totals =	$753.11		$835.1585	$835.16	$835.15	$835.00