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	$28.92	7.564%	$31.1075	$31.11	$31.10	$31.10
Purchase #2	$86.72	11.123%	$96.3659	$96.37	$96.35	$96.40
Purchase #3	$234.31	11.227%	$260.616	$260.62	$260.60	$260.60
Purchase #4	$198.52	4.686%	$207.8226	$207.82	$207.80	$207.80
Purchase #5	$33.61	11.388%	$37.4375	$37.44	$37.45	$37.40
Purchase #6	$156.74	7.346%	$168.2541	$168.25	$168.25	$168.30
Purchase #7	$97.50	6.545%	$103.8814	$103.88	$103.90	$103.90
7 purchase totals =	$836.32		$905.4850	$905.49	$905.45	$905.50