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	$239.27	12.829%	$269.9659	$269.97	$269.95	$270.00
Purchase #2	$35.46	13.318%	$40.1826	$40.18	$40.20	$40.20
Purchase #3	$206.62	7.157%	$221.4078	$221.41	$221.40	$221.40
Purchase #4	$54.32	10.213%	$59.8677	$59.87	$59.85	$59.90
Purchase #5	$204.84	6.392%	$217.9334	$217.93	$217.95	$217.90
Purchase #6	$24.57	13.294%	$27.8363	$27.84	$27.85	$27.80
Purchase #7	$38.33	5.137%	$40.299	$40.30	$40.30	$40.30
7 purchase totals =	$803.41		$877.4927	$877.50	$877.50	$877.50