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	$48.72	11.777%	$54.4578	$54.46	$54.45	$54.50
Purchase #2	$19.31	12.375%	$21.6996	$21.70	$21.70	$21.70
Purchase #3	$118.79	11.527%	$132.4829	$132.48	$132.50	$132.50
Purchase #4	$190.63	13.540%	$216.4413	$216.44	$216.45	$216.40
Purchase #5	$52.43	4.314%	$54.6918	$54.69	$54.70	$54.70
Purchase #6	$149.88	8.700%	$162.9196	$162.92	$162.90	$162.90
Purchase #7	$248.64	12.328%	$279.2923	$279.29	$279.30	$279.30
7 purchase totals =	$828.40		$921.9853	$921.98	$922.00	$922.00