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	$247.54	9.256%	$270.4523	$270.45	$270.45	$270.50
Purchase #2	$153.31	9.412%	$167.7395	$167.74	$167.75	$167.70
Purchase #3	$19.32	12.228%	$21.6824	$21.68	$21.70	$21.70
Purchase #4	$92.99	10.442%	$102.7	$102.70	$102.70	$102.70
Purchase #5	$50.53	13.364%	$57.2828	$57.28	$57.30	$57.30
Purchase #6	$80.68	12.398%	$90.6827	$90.68	$90.70	$90.70
Purchase #7	$113.61	8.710%	$123.5054	$123.51	$123.50	$123.50
7 purchase totals =	$757.98		$834.0451	$834.04	$834.10	$834.10