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	$98.25	4.440%	$102.6123	$102.61	$102.60	$102.60
Purchase #2	$62.38	3.220%	$64.3886	$64.39	$64.40	$64.40
Purchase #3	$82.88	3.582%	$85.8488	$85.85	$85.85	$85.80
Purchase #4	$236.54	11.418%	$263.5481	$263.55	$263.55	$263.50
Purchase #5	$117.98	13.856%	$134.3273	$134.33	$134.35	$134.30
Purchase #6	$178.60	8.826%	$194.3632	$194.36	$194.35	$194.40
Purchase #7	$124.87	6.866%	$133.4436	$133.44	$133.45	$133.40
7 purchase totals =	$901.50		$978.5319	$978.53	$978.55	$978.40