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	$107.73	6.476%	$114.7066	$114.71	$114.70	$114.70
Purchase #2	$130.86	8.596%	$142.1087	$142.11	$142.10	$142.10
Purchase #3	$67.50	7.484%	$72.5517	$72.55	$72.55	$72.60
Purchase #4	$9.73	12.861%	$10.9814	$10.98	$11.00	$11.00
Purchase #5	$89.99	10.711%	$99.6288	$99.63	$99.65	$99.60
Purchase #6	$128.48	12.519%	$144.5644	$144.56	$144.55	$144.60
Purchase #7	$150.61	3.118%	$155.306	$155.31	$155.30	$155.30
7 purchase totals =	$684.90		$739.8476	$739.85	$739.85	$739.90