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	$154.54	6.623%	$164.7752	$164.78	$164.80	$164.80
Purchase #2	$58.98	10.430%	$65.1316	$65.13	$65.15	$65.10
Purchase #3	$64.54	11.763%	$72.1318	$72.13	$72.15	$72.10
Purchase #4	$105.58	12.840%	$119.1365	$119.14	$119.15	$119.10
Purchase #5	$171.54	13.252%	$194.2725	$194.27	$194.25	$194.30
Purchase #6	$12.92	3.178%	$13.3306	$13.33	$13.35	$13.30
Purchase #7	$205.74	7.480%	$221.1294	$221.13	$221.15	$221.10
7 purchase totals =	$773.84		$849.9076	$849.91	$850.00	$849.80