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	$149.39	10.639%	$165.2836	$165.28	$165.30	$165.30
Purchase #2	$200.38	6.571%	$213.547	$213.55	$213.55	$213.50
Purchase #3	$24.43	12.488%	$27.4808	$27.48	$27.50	$27.50
Purchase #4	$6.53	7.526%	$7.0214	$7.02	$7.00	$7.00
Purchase #5	$78.31	12.228%	$87.8857	$87.89	$87.90	$87.90
Purchase #6	$151.49	4.869%	$158.866	$158.87	$158.85	$158.90
Purchase #7	$109.59	8.224%	$118.6027	$118.60	$118.60	$118.60
7 purchase totals =	$720.12		$778.6872	$778.69	$778.70	$778.70