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	$124.78	9.110%	$136.1475	$136.15	$136.15	$136.10
Purchase #2	$145.85	8.648%	$158.4631	$158.46	$158.45	$158.50
Purchase #3	$92.51	6.641%	$98.6536	$98.65	$98.65	$98.70
Purchase #4	$86.64	11.377%	$96.497	$96.50	$96.50	$96.50
Purchase #5	$145.60	4.649%	$152.3689	$152.37	$152.35	$152.40
Purchase #6	$31.85	5.811%	$33.7008	$33.70	$33.70	$33.70
Purchase #7	$31.90	11.340%	$35.5175	$35.52	$35.50	$35.50
7 purchase totals =	$659.13		$711.3484	$711.35	$711.30	$711.40