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	$90.95	10.190%	$100.2178	$100.22	$100.20	$100.20
Purchase #2	$82.56	7.358%	$88.6348	$88.63	$88.65	$88.60
Purchase #3	$130.38	11.387%	$145.2264	$145.23	$145.25	$145.20
Purchase #4	$198.55	5.643%	$209.7542	$209.75	$209.75	$209.80
Purchase #5	$233.45	13.870%	$265.8295	$265.83	$265.85	$265.80
Purchase #6	$9.43	13.659%	$10.718	$10.72	$10.70	$10.70
Purchase #7	$81.48	5.392%	$85.8734	$85.87	$85.85	$85.90
7 purchase totals =	$826.80		$906.2541	$906.25	$906.25	$906.20