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	$168.85	4.401%	$176.2811	$176.28	$176.30	$176.30
Purchase #2	$74.64	12.755%	$84.1603	$84.16	$84.15	$84.20
Purchase #3	$85.66	7.543%	$92.1213	$92.12	$92.10	$92.10
Purchase #4	$76.91	8.715%	$83.6127	$83.61	$83.60	$83.60
Purchase #5	$141.40	6.667%	$150.8271	$150.83	$150.85	$150.80
Purchase #6	$29.40	8.241%	$31.8229	$31.82	$31.80	$31.80
Purchase #7	$154.87	6.230%	$164.5184	$164.52	$164.50	$164.50
7 purchase totals =	$731.73		$783.3438	$783.34	$783.30	$783.30