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	$248.60	13.347%	$281.7806	$281.78	$281.80	$281.80
Purchase #2	$27.79	3.706%	$28.8199	$28.82	$28.80	$28.80
Purchase #3	$54.83	10.488%	$60.5806	$60.58	$60.60	$60.60
Purchase #4	$117.47	12.245%	$131.8542	$131.85	$131.85	$131.90
Purchase #5	$232.50	3.700%	$241.1025	$241.10	$241.10	$241.10
Purchase #6	$36.77	8.814%	$40.0109	$40.01	$40.00	$40.00
Purchase #7	$53.77	8.421%	$58.298	$58.30	$58.30	$58.30
7 purchase totals =	$771.73		$842.4467	$842.44	$842.45	$842.50