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	$52.28	12.683%	$58.9107	$58.91	$58.90	$58.90
Purchase #2	$11.88	13.554%	$13.4902	$13.49	$13.50	$13.50
Purchase #3	$70.25	3.742%	$72.8788	$72.88	$72.90	$72.90
Purchase #4	$152.38	5.613%	$160.9331	$160.93	$160.95	$160.90
Purchase #5	$244.46	7.135%	$261.9022	$261.90	$261.90	$261.90
Purchase #6	$244.89	5.770%	$259.0202	$259.02	$259.00	$259.00
Purchase #7	$245.60	11.400%	$273.5984	$273.60	$273.60	$273.60
7 purchase totals =	$1,021.74		$1,100.7336	$1,100.73	$1,100.75	$1,100.70