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	$70.58	13.367%	$80.0144	$80.01	$80.00	$80.00
Purchase #2	$99.51	11.759%	$111.2114	$111.21	$111.20	$111.20
Purchase #3	$127.33	13.850%	$144.9652	$144.97	$144.95	$145.00
Purchase #4	$67.80	3.740%	$70.3357	$70.34	$70.35	$70.30
Purchase #5	$206.85	11.131%	$229.8745	$229.87	$229.85	$229.90
Purchase #6	$205.87	9.455%	$225.335	$225.34	$225.35	$225.30
Purchase #7	$154.91	13.840%	$176.3495	$176.35	$176.35	$176.30
7 purchase totals =	$932.85		$1,038.0857	$1,038.09	$1,038.05	$1,038.00