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	$105.70	9.387%	$115.6221	$115.62	$115.60	$115.60
Purchase #2	$69.29	12.179%	$77.7288	$77.73	$77.75	$77.70
Purchase #3	$213.82	4.560%	$223.5702	$223.57	$223.55	$223.60
Purchase #4	$111.64	6.650%	$119.0641	$119.06	$119.05	$119.10
Purchase #5	$66.42	7.420%	$71.3484	$71.35	$71.35	$71.30
Purchase #6	$188.35	4.348%	$196.5395	$196.54	$196.55	$196.50
Purchase #7	$160.76	4.483%	$167.9669	$167.97	$167.95	$168.00
7 purchase totals =	$915.98		$971.8400	$971.84	$971.80	$971.80