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	$49.89	7.807%	$53.7849	$53.78	$53.80	$53.80
Purchase #2	$124.83	10.268%	$137.6475	$137.65	$137.65	$137.60
Purchase #3	$167.97	8.109%	$181.5907	$181.59	$181.60	$181.60
Purchase #4	$7.90	5.509%	$8.3352	$8.34	$8.35	$8.30
Purchase #5	$142.41	3.850%	$147.8928	$147.89	$147.90	$147.90
Purchase #6	$134.27	3.562%	$139.0527	$139.05	$139.05	$139.10
Purchase #7	$155.28	10.464%	$171.5285	$171.53	$171.55	$171.50
7 purchase totals =	$782.55		$839.8323	$839.83	$839.90	$839.80