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	$91.30	8.842%	$99.3727	$99.37	$99.35	$99.40
Purchase #2	$6.86	7.621%	$7.3828	$7.38	$7.40	$7.40
Purchase #3	$205.51	8.515%	$223.0092	$223.01	$223.00	$223.00
Purchase #4	$101.30	11.292%	$112.7388	$112.74	$112.75	$112.70
Purchase #5	$39.36	5.317%	$41.4528	$41.45	$41.45	$41.50
Purchase #6	$123.70	8.627%	$134.3716	$134.37	$134.35	$134.40
Purchase #7	$51.76	7.624%	$55.7062	$55.71	$55.70	$55.70
7 purchase totals =	$619.79		$674.0341	$674.03	$674.00	$674.10