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	$67.83	5.481%	$71.5478	$71.55	$71.55	$71.50
Purchase #2	$87.87	3.157%	$90.6441	$90.64	$90.65	$90.60
Purchase #3	$218.99	13.802%	$249.215	$249.22	$249.20	$249.20
Purchase #4	$6.63	11.659%	$7.403	$7.40	$7.40	$7.40
Purchase #5	$189.62	13.518%	$215.2528	$215.25	$215.25	$215.30
Purchase #6	$90.37	6.141%	$95.9196	$95.92	$95.90	$95.90
Purchase #7	$229.85	9.534%	$251.7639	$251.76	$251.75	$251.80
7 purchase totals =	$891.16		$981.7462	$981.74	$981.70	$981.70