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	$20.53	4.853%	$21.5263	$21.53	$21.55	$21.50
Purchase #2	$188.30	3.481%	$194.8547	$194.85	$194.85	$194.90
Purchase #3	$211.58	3.272%	$218.5029	$218.50	$218.50	$218.50
Purchase #4	$65.43	9.808%	$71.8474	$71.85	$71.85	$71.80
Purchase #5	$34.53	12.782%	$38.9436	$38.94	$38.95	$38.90
Purchase #6	$214.76	7.708%	$231.3137	$231.31	$231.30	$231.30
Purchase #7	$72.27	12.716%	$81.4599	$81.46	$81.45	$81.50
7 purchase totals =	$807.40		$858.4485	$858.44	$858.45	$858.40