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	$90.56	11.206%	$100.7082	$100.71	$100.70	$100.70
Purchase #2	$112.64	10.190%	$124.118	$124.12	$124.10	$124.10
Purchase #3	$174.55	11.654%	$194.8921	$194.89	$194.90	$194.90
Purchase #4	$44.78	8.664%	$48.6597	$48.66	$48.65	$48.70
Purchase #5	$88.54	7.197%	$94.9122	$94.91	$94.90	$94.90
Purchase #6	$144.44	4.287%	$150.6321	$150.63	$150.65	$150.60
Purchase #7	$164.67	5.574%	$173.8487	$173.85	$173.85	$173.80
7 purchase totals =	$820.18		$887.7710	$887.77	$887.75	$887.70