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	$68.97	13.732%	$78.441	$78.44	$78.45	$78.40
Purchase #2	$196.63	12.612%	$221.429	$221.43	$221.45	$221.40
Purchase #3	$176.72	4.241%	$184.2147	$184.21	$184.20	$184.20
Purchase #4	$176.31	3.782%	$182.978	$182.98	$183.00	$183.00
Purchase #5	$197.45	7.219%	$211.7039	$211.70	$211.70	$211.70
Purchase #6	$48.87	13.354%	$55.3961	$55.40	$55.40	$55.40
Purchase #7	$44.26	3.731%	$45.9113	$45.91	$45.90	$45.90
7 purchase totals =	$909.21		$980.0740	$980.07	$980.10	$980.00