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	$144.58	13.703%	$164.3918	$164.39	$164.40	$164.40
Purchase #2	$88.38	4.495%	$92.3527	$92.35	$92.35	$92.40
Purchase #3	$21.37	13.778%	$24.3144	$24.31	$24.30	$24.30
Purchase #4	$219.45	10.380%	$242.2289	$242.23	$242.25	$242.20
Purchase #5	$15.31	7.621%	$16.4768	$16.48	$16.50	$16.50
Purchase #6	$121.77	4.469%	$127.2119	$127.21	$127.20	$127.20
Purchase #7	$165.52	10.155%	$182.3286	$182.33	$182.35	$182.30
7 purchase totals =	$776.38		$849.3051	$849.30	$849.35	$849.30