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	$37.86	6.357%	$40.2668	$40.27	$40.25	$40.30
Purchase #2	$189.72	11.486%	$211.5112	$211.51	$211.50	$211.50
Purchase #3	$51.53	8.250%	$55.7812	$55.78	$55.80	$55.80
Purchase #4	$202.49	6.186%	$215.016	$215.02	$215.00	$215.00
Purchase #5	$247.91	7.780%	$267.1974	$267.20	$267.20	$267.20
Purchase #6	$182.43	7.667%	$196.4169	$196.42	$196.40	$196.40
Purchase #7	$72.61	8.327%	$78.6562	$78.66	$78.65	$78.70
7 purchase totals =	$984.55		$1,064.8457	$1,064.86	$1,064.80	$1,064.90