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	$134.93	7.165%	$144.5977	$144.60	$144.60	$144.60
Purchase #2	$80.92	3.134%	$83.456	$83.46	$83.45	$83.50
Purchase #3	$34.93	4.387%	$36.4624	$36.46	$36.45	$36.50
Purchase #4	$188.65	4.715%	$197.5448	$197.54	$197.55	$197.50
Purchase #5	$62.69	7.215%	$67.2131	$67.21	$67.20	$67.20
Purchase #6	$200.71	6.814%	$214.3864	$214.39	$214.40	$214.40
Purchase #7	$62.30	7.362%	$66.8865	$66.89	$66.90	$66.90
7 purchase totals =	$765.13		$810.5469	$810.55	$810.55	$810.60