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	$248.53	6.613%	$264.9653	$264.97	$264.95	$265.00
Purchase #2	$174.80	12.484%	$196.622	$196.62	$196.60	$196.60
Purchase #3	$54.47	6.251%	$57.8749	$57.87	$57.85	$57.90
Purchase #4	$156.43	12.840%	$176.5156	$176.52	$176.50	$176.50
Purchase #5	$78.59	6.525%	$83.718	$83.72	$83.70	$83.70
Purchase #6	$52.50	9.147%	$57.3022	$57.30	$57.30	$57.30
Purchase #7	$200.51	5.398%	$211.3335	$211.33	$211.35	$211.30
7 purchase totals =	$965.83		$1,048.3315	$1,048.33	$1,048.25	$1,048.30