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	$186.26	3.324%	$192.4513	$192.45	$192.45	$192.50
Purchase #2	$160.85	12.236%	$180.5316	$180.53	$180.55	$180.50
Purchase #3	$231.89	10.365%	$255.9254	$255.93	$255.95	$255.90
Purchase #4	$83.80	11.821%	$93.706	$93.71	$93.70	$93.70
Purchase #5	$104.90	4.715%	$109.846	$109.85	$109.85	$109.80
Purchase #6	$88.67	4.268%	$92.4544	$92.45	$92.45	$92.50
Purchase #7	$67.45	11.150%	$74.9707	$74.97	$74.95	$75.00
7 purchase totals =	$923.82		$999.8854	$999.89	$999.90	$999.90