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	$25.96	12.404%	$29.1801	$29.18	$29.20	$29.20
Purchase #2	$117.33	5.153%	$123.376	$123.38	$123.40	$123.40
Purchase #3	$167.36	12.472%	$188.2331	$188.23	$188.25	$188.20
Purchase #4	$224.33	8.660%	$243.757	$243.76	$243.75	$243.80
Purchase #5	$196.45	9.842%	$215.7846	$215.78	$215.80	$215.80
Purchase #6	$124.30	6.215%	$132.0252	$132.03	$132.05	$132.00
Purchase #7	$48.82	13.653%	$55.4854	$55.49	$55.50	$55.50
7 purchase totals =	$904.55		$987.8414	$987.85	$987.95	$987.90