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	$100.73	8.749%	$109.5429	$109.54	$109.55	$109.50
Purchase #2	$92.99	7.724%	$100.1725	$100.17	$100.15	$100.20
Purchase #3	$212.98	6.262%	$226.3168	$226.32	$226.30	$226.30
Purchase #4	$88.90	10.373%	$98.1216	$98.12	$98.10	$98.10
Purchase #5	$158.79	8.402%	$172.1315	$172.13	$172.15	$172.10
Purchase #6	$100.67	3.107%	$103.7978	$103.80	$103.80	$103.80
Purchase #7	$138.73	6.173%	$147.2938	$147.29	$147.30	$147.30
7 purchase totals =	$893.79		$957.3769	$957.37	$957.35	$957.30