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	$92.50	6.872%	$98.8566	$98.86	$98.85	$98.90
Purchase #2	$217.25	12.288%	$243.9457	$243.95	$243.95	$243.90
Purchase #3	$62.98	6.445%	$67.0391	$67.04	$67.05	$67.00
Purchase #4	$102.38	13.510%	$116.2115	$116.21	$116.20	$116.20
Purchase #5	$151.46	3.258%	$156.3946	$156.39	$156.40	$156.40
Purchase #6	$24.54	10.420%	$27.0971	$27.10	$27.10	$27.10
Purchase #7	$96.90	4.281%	$101.0483	$101.05	$101.05	$101.00
7 purchase totals =	$748.01		$810.5929	$810.60	$810.60	$810.50