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	$102.46	12.558%	$115.3269	$115.33	$115.35	$115.30
Purchase #2	$44.61	3.789%	$46.3003	$46.30	$46.30	$46.30
Purchase #3	$58.83	11.734%	$65.7331	$65.73	$65.75	$65.70
Purchase #4	$59.40	9.431%	$65.002	$65.00	$65.00	$65.00
Purchase #5	$7.40	5.185%	$7.7837	$7.78	$7.80	$7.80
Purchase #6	$201.52	5.556%	$212.7165	$212.72	$212.70	$212.70
Purchase #7	$37.42	11.274%	$41.6387	$41.64	$41.65	$41.60
7 purchase totals =	$511.64		$554.5012	$554.50	$554.55	$554.40