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	$39.69	4.292%	$41.3935	$41.39	$41.40	$41.40
Purchase #2	$194.42	4.316%	$202.8112	$202.81	$202.80	$202.80
Purchase #3	$156.36	7.747%	$168.4732	$168.47	$168.45	$168.50
Purchase #4	$201.91	10.296%	$222.6987	$222.70	$222.70	$222.70
Purchase #5	$189.37	13.392%	$214.7304	$214.73	$214.75	$214.70
Purchase #6	$123.51	13.283%	$139.9158	$139.92	$139.90	$139.90
Purchase #7	$11.91	13.326%	$13.4971	$13.50	$13.50	$13.50
7 purchase totals =	$917.17		$1,003.5199	$1,003.52	$1,003.50	$1,003.50