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	$131.89	7.605%	$141.9202	$141.92	$141.90	$141.90
Purchase #2	$82.78	6.465%	$88.1317	$88.13	$88.15	$88.10
Purchase #3	$168.71	9.270%	$184.3494	$184.35	$184.35	$184.30
Purchase #4	$137.51	8.124%	$148.6813	$148.68	$148.70	$148.70
Purchase #5	$41.98	3.663%	$43.5177	$43.52	$43.50	$43.50
Purchase #6	$112.95	12.327%	$126.8733	$126.87	$126.85	$126.90
Purchase #7	$40.90	13.481%	$46.4137	$46.41	$46.40	$46.40
7 purchase totals =	$716.72		$779.8873	$779.88	$779.85	$779.80