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	$22.56	12.666%	$25.4174	$25.42	$25.40	$25.40
Purchase #2	$35.37	4.646%	$37.0133	$37.01	$37.00	$37.00
Purchase #3	$175.52	5.626%	$185.3948	$185.39	$185.40	$185.40
Purchase #4	$208.41	12.632%	$234.7364	$234.74	$234.75	$234.70
Purchase #5	$128.62	13.815%	$146.3889	$146.39	$146.40	$146.40
Purchase #6	$118.36	4.775%	$124.0117	$124.01	$124.00	$124.00
Purchase #7	$41.78	13.838%	$47.5615	$47.56	$47.55	$47.60
7 purchase totals =	$730.62		$800.5240	$800.52	$800.50	$800.50