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	$123.32	11.783%	$137.8508	$137.85	$137.85	$137.90
Purchase #2	$235.76	12.353%	$264.8834	$264.88	$264.90	$264.90
Purchase #3	$223.64	9.807%	$245.5724	$245.57	$245.55	$245.60
Purchase #4	$234.72	4.832%	$246.0617	$246.06	$246.05	$246.10
Purchase #5	$44.43	4.630%	$46.4871	$46.49	$46.50	$46.50
Purchase #6	$37.81	13.598%	$42.9514	$42.95	$42.95	$43.00
Purchase #7	$79.97	13.557%	$90.8115	$90.81	$90.80	$90.80
7 purchase totals =	$979.65		$1,074.6183	$1,074.61	$1,074.60	$1,074.80