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	$247.38	4.512%	$258.5418	$258.54	$258.55	$258.50
Purchase #2	$237.48	4.234%	$247.5349	$247.53	$247.55	$247.50
Purchase #3	$176.82	7.176%	$189.5086	$189.51	$189.50	$189.50
Purchase #4	$101.83	5.585%	$107.5172	$107.52	$107.50	$107.50
Purchase #5	$115.94	6.162%	$123.0842	$123.08	$123.10	$123.10
Purchase #6	$37.59	12.814%	$42.4068	$42.41	$42.40	$42.40
Purchase #7	$11.42	13.299%	$12.9387	$12.94	$12.95	$12.90
7 purchase totals =	$928.46		$981.5322	$981.53	$981.55	$981.40