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	$108.57	12.639%	$122.2922	$122.29	$122.30	$122.30
Purchase #2	$234.41	6.783%	$250.31	$250.31	$250.30	$250.30
Purchase #3	$11.44	8.228%	$12.3813	$12.38	$12.40	$12.40
Purchase #4	$23.26	5.262%	$24.4839	$24.48	$24.50	$24.50
Purchase #5	$104.63	6.179%	$111.0951	$111.10	$111.10	$111.10
Purchase #6	$108.46	13.718%	$123.3385	$123.34	$123.35	$123.30
Purchase #7	$154.96	4.728%	$162.2865	$162.29	$162.30	$162.30
7 purchase totals =	$745.73		$806.1875	$806.19	$806.25	$806.20