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	$48.79	13.660%	$55.4547	$55.45	$55.45	$55.50
Purchase #2	$154.34	6.543%	$164.4385	$164.44	$164.45	$164.40
Purchase #3	$250.46	6.618%	$267.0354	$267.04	$267.05	$267.00
Purchase #4	$153.57	4.228%	$160.0629	$160.06	$160.05	$160.10
Purchase #5	$93.70	6.567%	$99.8533	$99.85	$99.85	$99.90
Purchase #6	$97.47	3.515%	$100.8961	$100.90	$100.90	$100.90
Purchase #7	$223.85	12.553%	$251.9499	$251.95	$251.95	$251.90
7 purchase totals =	$1,022.18		$1,099.6908	$1,099.69	$1,099.70	$1,099.70