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	$64.76	9.813%	$71.1149	$71.11	$71.10	$71.10
Purchase #2	$62.53	12.716%	$70.4813	$70.48	$70.50	$70.50
Purchase #3	$169.33	6.754%	$180.7665	$180.77	$180.75	$180.80
Purchase #4	$20.60	3.123%	$21.2433	$21.24	$21.25	$21.20
Purchase #5	$191.78	3.526%	$198.5422	$198.54	$198.55	$198.50
Purchase #6	$23.85	4.266%	$24.8674	$24.87	$24.85	$24.90
Purchase #7	$104.92	7.585%	$112.8782	$112.88	$112.90	$112.90
7 purchase totals =	$637.77		$679.8938	$679.89	$679.90	$679.90