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	$82.75	9.185%	$90.3506	$90.35	$90.35	$90.40
Purchase #2	$92.37	13.601%	$104.9332	$104.93	$104.95	$104.90
Purchase #3	$222.88	9.608%	$244.2943	$244.29	$244.30	$244.30
Purchase #4	$238.85	10.252%	$263.3369	$263.34	$263.35	$263.30
Purchase #5	$114.31	4.823%	$119.8232	$119.82	$119.80	$119.80
Purchase #6	$54.69	9.601%	$59.9408	$59.94	$59.95	$59.90
Purchase #7	$220.26	4.311%	$229.7554	$229.76	$229.75	$229.80
7 purchase totals =	$1,026.11		$1,112.4344	$1,112.43	$1,112.45	$1,112.40