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	$48.50	13.216%	$54.9098	$54.91	$54.90	$54.90
Purchase #2	$49.82	11.473%	$55.5358	$55.54	$55.55	$55.50
Purchase #3	$133.56	5.438%	$140.823	$140.82	$140.80	$140.80
Purchase #4	$169.63	5.495%	$178.9512	$178.95	$178.95	$179.00
Purchase #5	$44.40	13.647%	$50.4593	$50.46	$50.45	$50.50
Purchase #6	$201.89	6.612%	$215.239	$215.24	$215.25	$215.20
Purchase #7	$200.51	8.686%	$217.9263	$217.93	$217.95	$217.90
7 purchase totals =	$848.31		$913.8444	$913.85	$913.85	$913.80