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	$82.67	10.272%	$91.1619	$91.16	$91.15	$91.20
Purchase #2	$144.56	7.216%	$154.9914	$154.99	$155.00	$155.00
Purchase #3	$179.59	6.651%	$191.5345	$191.53	$191.55	$191.50
Purchase #4	$28.78	9.508%	$31.5164	$31.52	$31.50	$31.50
Purchase #5	$104.36	7.163%	$111.8353	$111.84	$111.85	$111.80
Purchase #6	$174.67	12.500%	$196.5038	$196.50	$196.50	$196.50
Purchase #7	$164.57	7.734%	$177.2978	$177.30	$177.30	$177.30
7 purchase totals =	$879.20		$954.8411	$954.84	$954.85	$954.80