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	$65.40	8.183%	$70.7517	$70.75	$70.75	$70.80
Purchase #2	$51.68	9.414%	$56.5452	$56.55	$56.55	$56.50
Purchase #3	$213.63	12.378%	$240.0731	$240.07	$240.05	$240.10
Purchase #4	$231.90	4.118%	$241.4496	$241.45	$241.45	$241.40
Purchase #5	$223.45	4.318%	$233.0986	$233.10	$233.10	$233.10
Purchase #6	$133.69	6.690%	$142.6339	$142.63	$142.65	$142.60
Purchase #7	$93.94	8.487%	$101.9127	$101.91	$101.90	$101.90
7 purchase totals =	$1,013.69		$1,086.4648	$1,086.46	$1,086.45	$1,086.40