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	$226.31	13.521%	$256.9094	$256.91	$256.90	$256.90
Purchase #2	$95.75	11.209%	$106.4826	$106.48	$106.50	$106.50
Purchase #3	$230.81	12.215%	$259.0034	$259.00	$259.00	$259.00
Purchase #4	$38.44	13.706%	$43.7086	$43.71	$43.70	$43.70
Purchase #5	$175.53	11.659%	$195.995	$196.00	$196.00	$196.00
Purchase #6	$176.34	3.171%	$181.9317	$181.93	$181.95	$181.90
Purchase #7	$28.57	6.661%	$30.473	$30.47	$30.45	$30.50
7 purchase totals =	$971.75		$1,074.5037	$1,074.50	$1,074.50	$1,074.50