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	$142.48	4.159%	$148.4057	$148.41	$148.40	$148.40
Purchase #2	$37.68	5.711%	$39.8319	$39.83	$39.85	$39.80
Purchase #3	$84.51	5.396%	$89.0702	$89.07	$89.05	$89.10
Purchase #4	$185.89	7.734%	$200.2667	$200.27	$200.25	$200.30
Purchase #5	$45.90	7.266%	$49.2351	$49.24	$49.25	$49.20
Purchase #6	$108.33	6.470%	$115.339	$115.34	$115.35	$115.30
Purchase #7	$172.95	3.682%	$179.318	$179.32	$179.30	$179.30
7 purchase totals =	$777.74		$821.4666	$821.48	$821.45	$821.40