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	$49.98	5.770%	$52.8638	$52.86	$52.85	$52.90
Purchase #2	$151.30	11.629%	$168.8947	$168.89	$168.90	$168.90
Purchase #3	$152.52	7.731%	$164.3113	$164.31	$164.30	$164.30
Purchase #4	$109.42	11.475%	$121.9759	$121.98	$122.00	$122.00
Purchase #5	$191.28	6.368%	$203.4607	$203.46	$203.45	$203.50
Purchase #6	$90.95	3.291%	$93.9432	$93.94	$93.95	$93.90
Purchase #7	$128.94	11.666%	$143.9821	$143.98	$144.00	$144.00
7 purchase totals =	$874.39		$949.4317	$949.42	$949.45	$949.50