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	$41.61	3.860%	$43.2161	$43.22	$43.20	$43.20
Purchase #2	$167.46	9.839%	$183.9364	$183.94	$183.95	$183.90
Purchase #3	$24.27	13.512%	$27.5494	$27.55	$27.55	$27.50
Purchase #4	$70.59	12.371%	$79.3227	$79.32	$79.30	$79.30
Purchase #5	$179.38	3.136%	$185.0054	$185.01	$185.00	$185.00
Purchase #6	$38.89	13.677%	$44.209	$44.21	$44.20	$44.20
Purchase #7	$230.33	9.865%	$253.0521	$253.05	$253.05	$253.10
7 purchase totals =	$752.53		$816.2911	$816.30	$816.25	$816.20