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	$43.32	4.615%	$45.3192	$45.32	$45.30	$45.30
Purchase #2	$18.70	12.304%	$21.0008	$21.00	$21.00	$21.00
Purchase #3	$218.41	8.314%	$236.5686	$236.57	$236.55	$236.60
Purchase #4	$155.28	10.718%	$171.9229	$171.92	$171.90	$171.90
Purchase #5	$57.52	8.358%	$62.3275	$62.33	$62.35	$62.30
Purchase #6	$149.85	4.388%	$156.4254	$156.43	$156.45	$156.40
Purchase #7	$143.94	3.127%	$148.441	$148.44	$148.45	$148.40
7 purchase totals =	$787.02		$842.0054	$842.01	$842.00	$841.90