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	$222.89	10.510%	$246.3157	$246.32	$246.30	$246.30
Purchase #2	$169.69	6.434%	$180.6079	$180.61	$180.60	$180.60
Purchase #3	$147.96	13.187%	$167.4715	$167.47	$167.45	$167.50
Purchase #4	$173.58	3.293%	$179.296	$179.30	$179.30	$179.30
Purchase #5	$51.33	12.134%	$57.5584	$57.56	$57.55	$57.60
Purchase #6	$104.46	7.477%	$112.2705	$112.27	$112.25	$112.30
Purchase #7	$227.47	5.258%	$239.4304	$239.43	$239.45	$239.40
7 purchase totals =	$1,097.38		$1,182.9504	$1,182.96	$1,182.90	$1,183.00