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	$143.50	8.141%	$155.1823	$155.18	$155.20	$155.20
Purchase #2	$225.98	6.863%	$241.489	$241.49	$241.50	$241.50
Purchase #3	$33.67	12.320%	$37.8181	$37.82	$37.80	$37.80
Purchase #4	$38.32	8.130%	$41.4354	$41.44	$41.45	$41.40
Purchase #5	$67.48	8.510%	$73.2225	$73.22	$73.20	$73.20
Purchase #6	$218.87	4.119%	$227.8853	$227.89	$227.90	$227.90
Purchase #7	$69.96	3.802%	$72.6199	$72.62	$72.60	$72.60
7 purchase totals =	$797.78		$849.6525	$849.66	$849.65	$849.60