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	$97.25	10.289%	$107.2561	$107.26	$107.25	$107.30
Purchase #2	$139.87	12.132%	$156.839	$156.84	$156.85	$156.80
Purchase #3	$132.63	4.684%	$138.8424	$138.84	$138.85	$138.80
Purchase #4	$190.72	10.144%	$210.0666	$210.07	$210.05	$210.10
Purchase #5	$247.95	3.364%	$256.291	$256.29	$256.30	$256.30
Purchase #6	$19.25	13.579%	$21.864	$21.86	$21.85	$21.90
Purchase #7	$104.76	6.813%	$111.8973	$111.90	$111.90	$111.90
7 purchase totals =	$932.43		$1,003.0564	$1,003.06	$1,003.05	$1,003.10