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	$57.89	6.185%	$61.4705	$61.47	$61.45	$61.50
Purchase #2	$54.48	9.803%	$59.8207	$59.82	$59.80	$59.80
Purchase #3	$148.40	13.768%	$168.8317	$168.83	$168.85	$168.80
Purchase #4	$59.97	5.739%	$63.4117	$63.41	$63.40	$63.40
Purchase #5	$112.35	12.488%	$126.3803	$126.38	$126.40	$126.40
Purchase #6	$78.28	12.675%	$88.202	$88.20	$88.20	$88.20
Purchase #7	$97.39	7.479%	$104.6738	$104.67	$104.65	$104.70
7 purchase totals =	$608.76		$672.7907	$672.78	$672.75	$672.80