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	$109.87	12.164%	$123.2346	$123.23	$123.25	$123.20
Purchase #2	$84.53	5.329%	$89.0346	$89.03	$89.05	$89.00
Purchase #3	$100.88	9.773%	$110.739	$110.74	$110.75	$110.70
Purchase #4	$225.68	13.192%	$255.4517	$255.45	$255.45	$255.50
Purchase #5	$47.97	13.481%	$54.4368	$54.44	$54.45	$54.40
Purchase #6	$71.99	12.616%	$81.0723	$81.07	$81.05	$81.10
Purchase #7	$84.56	10.748%	$93.6485	$93.65	$93.65	$93.60
7 purchase totals =	$725.48		$807.6175	$807.61	$807.65	$807.50