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	$20.29	6.360%	$21.5804	$21.58	$21.60	$21.60
Purchase #2	$222.37	11.202%	$247.2799	$247.28	$247.30	$247.30
Purchase #3	$115.46	12.801%	$130.24	$130.24	$130.25	$130.20
Purchase #4	$247.94	4.677%	$259.5362	$259.54	$259.55	$259.50
Purchase #5	$238.64	9.208%	$260.614	$260.61	$260.60	$260.60
Purchase #6	$76.51	11.389%	$85.2237	$85.22	$85.20	$85.20
Purchase #7	$235.50	12.498%	$264.9328	$264.93	$264.95	$264.90
7 purchase totals =	$1,156.71		$1,269.4070	$1,269.40	$1,269.45	$1,269.30