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	$61.73	8.732%	$67.1203	$67.12	$67.10	$67.10
Purchase #2	$58.45	6.744%	$62.3919	$62.39	$62.40	$62.40
Purchase #3	$133.92	10.115%	$147.466	$147.47	$147.45	$147.50
Purchase #4	$64.99	3.671%	$67.3758	$67.38	$67.40	$67.40
Purchase #5	$70.91	7.862%	$76.4849	$76.48	$76.50	$76.50
Purchase #6	$45.40	13.174%	$51.381	$51.38	$51.40	$51.40
Purchase #7	$88.59	3.713%	$91.8793	$91.88	$91.90	$91.90
7 purchase totals =	$523.99		$564.0992	$564.10	$564.15	$564.20