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	7.809%	$257.9546	$257.95	$257.95	$258.00
Purchase #2	$64.58	4.402%	$67.4228	$67.42	$67.40	$67.40
Purchase #3	$127.81	13.700%	$145.32	$145.32	$145.30	$145.30
Purchase #4	$226.65	10.528%	$250.5117	$250.51	$250.50	$250.50
Purchase #5	$239.30	7.345%	$256.8766	$256.88	$256.90	$256.90
Purchase #6	$237.37	5.283%	$249.9103	$249.91	$249.90	$249.90
Purchase #7	$72.59	9.592%	$79.5528	$79.55	$79.55	$79.60
7 purchase totals =	$1,207.57		$1,307.5488	$1,307.54	$1,307.50	$1,307.60