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	$69.82	12.456%	$78.5168	$78.52	$78.50	$78.50
Purchase #2	$205.93	11.299%	$229.198	$229.20	$229.20	$229.20
Purchase #3	$31.74	5.288%	$33.4184	$33.42	$33.40	$33.40
Purchase #4	$241.57	9.422%	$264.3307	$264.33	$264.35	$264.30
Purchase #5	$229.54	13.687%	$260.9571	$260.96	$260.95	$261.00
Purchase #6	$242.53	12.785%	$273.5375	$273.54	$273.55	$273.50
Purchase #7	$132.51	3.612%	$137.2963	$137.30	$137.30	$137.30
7 purchase totals =	$1,153.64		$1,277.2548	$1,277.27	$1,277.25	$1,277.20