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	$71.85	12.471%	$80.8104	$80.81	$80.80	$80.80
Purchase #2	$227.39	7.528%	$244.5079	$244.51	$244.50	$244.50
Purchase #3	$248.59	6.430%	$264.5743	$264.57	$264.55	$264.60
Purchase #4	$183.78	13.627%	$208.8237	$208.82	$208.80	$208.80
Purchase #5	$36.88	8.260%	$39.9263	$39.93	$39.95	$39.90
Purchase #6	$158.68	5.823%	$167.9199	$167.92	$167.90	$167.90
Purchase #7	$95.92	9.341%	$104.8799	$104.88	$104.90	$104.90
7 purchase totals =	$1,023.09		$1,111.4424	$1,111.44	$1,111.40	$1,111.40