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	$114.35	12.150%	$128.2435	$128.24	$128.25	$128.20
Purchase #2	$71.78	11.741%	$80.2077	$80.21	$80.20	$80.20
Purchase #3	$196.83	10.608%	$217.7097	$217.71	$217.70	$217.70
Purchase #4	$113.29	3.184%	$116.8972	$116.90	$116.90	$116.90
Purchase #5	$159.47	12.423%	$179.281	$179.28	$179.30	$179.30
Purchase #6	$119.85	12.356%	$134.6587	$134.66	$134.65	$134.70
Purchase #7	$143.61	10.801%	$159.1213	$159.12	$159.10	$159.10
7 purchase totals =	$919.18		$1,016.1191	$1,016.12	$1,016.10	$1,016.10