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	$213.54	3.161%	$220.29	$220.29	$220.30	$220.30
Purchase #2	$198.76	12.626%	$223.8554	$223.86	$223.85	$223.90
Purchase #3	$241.60	3.262%	$249.481	$249.48	$249.50	$249.50
Purchase #4	$151.71	3.392%	$156.856	$156.86	$156.85	$156.90
Purchase #5	$83.46	7.842%	$90.0049	$90.00	$90.00	$90.00
Purchase #6	$101.33	7.221%	$108.647	$108.65	$108.65	$108.60
Purchase #7	$99.77	6.784%	$106.5384	$106.54	$106.55	$106.50
7 purchase totals =	$1,090.17		$1,155.6727	$1,155.68	$1,155.70	$1,155.70