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	$229.82	3.689%	$238.2981	$238.30	$238.30	$238.30
Purchase #2	$228.97	9.231%	$250.1062	$250.11	$250.10	$250.10
Purchase #3	$12.39	11.629%	$13.8308	$13.83	$13.85	$13.80
Purchase #4	$19.55	10.490%	$21.6008	$21.60	$21.60	$21.60
Purchase #5	$12.73	6.856%	$13.6028	$13.60	$13.60	$13.60
Purchase #6	$213.99	13.119%	$242.0633	$242.06	$242.05	$242.10
Purchase #7	$218.68	12.644%	$246.3299	$246.33	$246.35	$246.30
7 purchase totals =	$936.13		$1,025.8319	$1,025.83	$1,025.85	$1,025.80