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	$94.82	4.565%	$99.1485	$99.15	$99.15	$99.10
Purchase #2	$123.37	10.475%	$136.293	$136.29	$136.30	$136.30
Purchase #3	$148.56	7.868%	$160.2487	$160.25	$160.25	$160.20
Purchase #4	$89.49	10.185%	$98.6046	$98.60	$98.60	$98.60
Purchase #5	$109.34	8.738%	$118.8941	$118.89	$118.90	$118.90
Purchase #6	$42.34	6.140%	$44.9397	$44.94	$44.95	$44.90
Purchase #7	$106.50	11.730%	$118.9925	$118.99	$119.00	$119.00
7 purchase totals =	$714.42		$777.1211	$777.11	$777.15	$777.00