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	$107.33	5.183%	$112.8929	$112.89	$112.90	$112.90
Purchase #2	$224.91	11.295%	$250.3136	$250.31	$250.30	$250.30
Purchase #3	$222.97	5.360%	$234.9212	$234.92	$234.90	$234.90
Purchase #4	$16.57	7.519%	$17.8159	$17.82	$17.80	$17.80
Purchase #5	$233.73	3.491%	$241.8895	$241.89	$241.90	$241.90
Purchase #6	$43.43	4.485%	$45.3778	$45.38	$45.40	$45.40
Purchase #7	$189.58	12.824%	$213.8917	$213.89	$213.90	$213.90
7 purchase totals =	$1,038.52		$1,117.1026	$1,117.10	$1,117.10	$1,117.10