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	$40.72	4.647%	$42.6123	$42.61	$42.60	$42.60
Purchase #2	$8.39	3.376%	$8.6732	$8.67	$8.65	$8.70
Purchase #3	$41.42	10.549%	$45.7894	$45.79	$45.80	$45.80
Purchase #4	$246.98	10.664%	$273.3179	$273.32	$273.30	$273.30
Purchase #5	$78.90	12.658%	$88.8872	$88.89	$88.90	$88.90
Purchase #6	$46.70	10.625%	$51.6619	$51.66	$51.65	$51.70
Purchase #7	$209.58	8.285%	$226.9437	$226.94	$226.95	$226.90
7 purchase totals =	$672.69		$737.8856	$737.88	$737.85	$737.90