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	$150.75	6.349%	$160.3211	$160.32	$160.30	$160.30
Purchase #2	$79.84	7.381%	$85.733	$85.73	$85.75	$85.70
Purchase #3	$83.50	3.153%	$86.1328	$86.13	$86.15	$86.10
Purchase #4	$178.76	7.160%	$191.5592	$191.56	$191.55	$191.60
Purchase #5	$128.51	11.666%	$143.502	$143.50	$143.50	$143.50
Purchase #6	$141.53	5.467%	$149.2674	$149.27	$149.25	$149.30
Purchase #7	$104.93	10.681%	$116.1376	$116.14	$116.15	$116.10
7 purchase totals =	$867.82		$932.6531	$932.65	$932.65	$932.60