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	$81.66	9.392%	$89.3295	$89.33	$89.35	$89.30
Purchase #2	$43.31	5.457%	$45.6734	$45.67	$45.65	$45.70
Purchase #3	$109.40	3.264%	$112.9708	$112.97	$112.95	$113.00
Purchase #4	$93.32	5.839%	$98.769	$98.77	$98.75	$98.80
Purchase #5	$107.98	10.771%	$119.6105	$119.61	$119.60	$119.60
Purchase #6	$81.30	13.133%	$91.9771	$91.98	$92.00	$92.00
Purchase #7	$36.68	10.196%	$40.4199	$40.42	$40.40	$40.40
7 purchase totals =	$553.65		$598.7502	$598.75	$598.70	$598.80