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	$66.50	8.628%	$72.2376	$72.24	$72.25	$72.20
Purchase #2	$47.67	12.736%	$53.7413	$53.74	$53.75	$53.70
Purchase #3	$187.61	13.386%	$212.7235	$212.72	$212.70	$212.70
Purchase #4	$98.25	4.373%	$102.5465	$102.55	$102.55	$102.50
Purchase #5	$33.68	12.706%	$37.9594	$37.96	$37.95	$38.00
Purchase #6	$37.78	5.347%	$39.8001	$39.80	$39.80	$39.80
Purchase #7	$136.35	8.791%	$148.3365	$148.34	$148.35	$148.30
7 purchase totals =	$607.84		$667.3449	$667.35	$667.35	$667.20