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	$25.65	11.725%	$28.6575	$28.66	$28.65	$28.70
Purchase #2	$181.79	5.454%	$191.7048	$191.70	$191.70	$191.70
Purchase #3	$22.80	13.506%	$25.8794	$25.88	$25.90	$25.90
Purchase #4	$87.44	3.600%	$90.5878	$90.59	$90.60	$90.60
Purchase #5	$36.38	13.194%	$41.18	$41.18	$41.20	$41.20
Purchase #6	$69.64	13.254%	$78.8701	$78.87	$78.85	$78.90
Purchase #7	$229.40	12.698%	$258.5292	$258.53	$258.55	$258.50
7 purchase totals =	$653.10		$715.4088	$715.41	$715.45	$715.50