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	$31.35	7.111%	$33.5793	$33.58	$33.60	$33.60
Purchase #2	$187.99	9.827%	$206.4638	$206.46	$206.45	$206.50
Purchase #3	$36.33	8.839%	$39.5412	$39.54	$39.55	$39.50
Purchase #4	$117.38	5.167%	$123.445	$123.45	$123.45	$123.40
Purchase #5	$192.67	6.453%	$205.103	$205.10	$205.10	$205.10
Purchase #6	$127.36	9.486%	$139.4414	$139.44	$139.45	$139.40
Purchase #7	$96.82	9.358%	$105.8804	$105.88	$105.90	$105.90
7 purchase totals =	$789.90		$853.4541	$853.45	$853.50	$853.40