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	$28.71	12.459%	$32.287	$32.29	$32.30	$32.30
Purchase #2	$249.63	5.549%	$263.482	$263.48	$263.50	$263.50
Purchase #3	$51.61	11.423%	$57.5054	$57.51	$57.50	$57.50
Purchase #4	$140.63	13.617%	$159.7796	$159.78	$159.80	$159.80
Purchase #5	$90.26	11.325%	$100.4819	$100.48	$100.50	$100.50
Purchase #6	$179.81	10.437%	$198.5768	$198.58	$198.60	$198.60
Purchase #7	$175.68	12.190%	$197.0954	$197.10	$197.10	$197.10
7 purchase totals =	$916.33		$1,009.2081	$1,009.22	$1,009.30	$1,009.30