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	$70.64	13.874%	$80.4406	$80.44	$80.45	$80.40
Purchase #2	$216.94	3.375%	$224.2617	$224.26	$224.25	$224.30
Purchase #3	$54.51	4.292%	$56.8496	$56.85	$56.85	$56.80
Purchase #4	$30.45	3.580%	$31.5401	$31.54	$31.55	$31.50
Purchase #5	$215.54	3.505%	$223.0947	$223.09	$223.10	$223.10
Purchase #6	$199.90	5.778%	$211.4502	$211.45	$211.45	$211.50
Purchase #7	$46.59	10.561%	$51.5104	$51.51	$51.50	$51.50
7 purchase totals =	$834.57		$879.1473	$879.14	$879.15	$879.10