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	$18.40	13.790%	$20.9374	$20.94	$20.95	$20.90
Purchase #2	$90.38	10.665%	$100.019	$100.02	$100.00	$100.00
Purchase #3	$150.51	13.655%	$171.0621	$171.06	$171.05	$171.10
Purchase #4	$92.27	13.300%	$104.5419	$104.54	$104.55	$104.50
Purchase #5	$178.45	8.611%	$193.8163	$193.82	$193.80	$193.80
Purchase #6	$66.32	8.808%	$72.1615	$72.16	$72.15	$72.20
Purchase #7	$100.72	5.677%	$106.4379	$106.44	$106.45	$106.40
7 purchase totals =	$697.05		$768.9761	$768.98	$768.95	$768.90