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	$142.57	9.646%	$156.3223	$156.32	$156.30	$156.30
Purchase #2	$124.49	10.657%	$137.7569	$137.76	$137.75	$137.80
Purchase #3	$127.85	9.607%	$140.1325	$140.13	$140.15	$140.10
Purchase #4	$80.79	12.207%	$90.652	$90.65	$90.65	$90.70
Purchase #5	$41.87	8.824%	$45.5646	$45.56	$45.55	$45.60
Purchase #6	$84.63	5.643%	$89.4057	$89.41	$89.40	$89.40
Purchase #7	$120.42	8.534%	$130.6966	$130.70	$130.70	$130.70
7 purchase totals =	$722.62		$790.5306	$790.53	$790.50	$790.60