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	$114.60	13.215%	$129.7444	$129.74	$129.75	$129.70
Purchase #2	$78.74	3.451%	$81.4573	$81.46	$81.45	$81.50
Purchase #3	$86.90	6.265%	$92.3443	$92.34	$92.35	$92.30
Purchase #4	$222.83	12.342%	$250.3317	$250.33	$250.35	$250.30
Purchase #5	$81.32	10.749%	$90.0611	$90.06	$90.05	$90.10
Purchase #6	$40.85	4.645%	$42.7475	$42.75	$42.75	$42.70
Purchase #7	$187.83	9.701%	$206.0514	$206.05	$206.05	$206.10
7 purchase totals =	$813.07		$892.7377	$892.73	$892.75	$892.70