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	$35.27	8.837%	$38.3868	$38.39	$38.40	$38.40
Purchase #2	$161.37	4.709%	$168.9689	$168.97	$168.95	$169.00
Purchase #3	$152.83	12.427%	$171.8222	$171.82	$171.80	$171.80
Purchase #4	$63.36	4.390%	$66.1415	$66.14	$66.15	$66.10
Purchase #5	$203.34	9.618%	$222.8972	$222.90	$222.90	$222.90
Purchase #6	$77.97	9.637%	$85.484	$85.48	$85.50	$85.50
Purchase #7	$54.31	12.129%	$60.8973	$60.90	$60.90	$60.90
7 purchase totals =	$748.45		$814.5979	$814.60	$814.60	$814.60